Apologies in advance for the massive post!
I think the squad will probably be 40 and I've taken some real punts on fitness etc. but assuming players are injury free and in good form, my squad would be:
1. M. Vunipola / McGrath / Marler
2. Hartley / Best / George
3. Cole / Nel / Hill
4. Itoje / Launchbury / J. Gray
5. Jones / Kruis / Henderson
6. O'Mahony / Robshaw
7. O'Brien / Warburton / Tipuric
8. Faletau / B. Vunipola
9. Webb / Murray / Youngs
10. Ford / Farrell / Sexton
11. North / May
12. Henshaw / Tuilagi
13. Joseph / Davies
14. Watson / Seymour / Nowell
15. Hogg / Halfpenny / Williams
I definitely don't think it's a given that O'Mahoney, O'Brien and Tuilagi can find peak fitness and form, but if they can, they're arguably the best available option in each position.
By position, my thoughts are as follows:
Loosehead:
Personally, I'd regard this as one of the easier choices as I think Mako, McGrath and Marler (in any order depending on form) are the three best in their position. Alistair Dickinson and Rob Evans are good, solid players, but I wouldn't put them on quite the same level. Cian Healy can't be disregarded altogether, but he's not been the same player following his injuries and as he's in direct competition with McGrath for both club and country, I think he's got an uphill struggle to make it. Like OldHooker, I think Genge has huge potential, but this tour is way too soon IMO. He would need to be starting regularly for Tigers and leapfrog Mako/Marler with England to be in with a shout and I think that's unlikely.
Hooker:
IMO, Hartley, Best and George are the top three Lions Hookers right now and personally, I don't think Baldwin or Owens offer anything better or different to warrant breaking up that pecking order. Ross Ford is a complete NO for me.
If Gatland wants to go for an impact sub, there are some interesting possibles. I'm excited to see Tom Youngs this year. I think it's easy to forget how good he was at points pre-injury and if he can demonstrate that he's managed to improve the weaker parts of his game and has a great season with Leicester, he could go ahead of George (irrespective of Eddie Jones' pecking order). Also Sean Cronin's ability as a pure impact sub is definitely worth considering as a wildcard option.
Tighthead:
Assuming they are fit, Cole and Nel are both in the match-day 23 and I'm fairly ambivalent over who starts. As Toby said, the third Tighthead spot is definitely up for grabs. I think Paul Hill will establish himself as first choice for Saints and as Cole's understudy for England this season. I also think he has a stronger all-round game than his main competitors. However, if Gatland prioritises the set-piece, then Mike Ross' experience could be valuable and Samson Lee will definitely be challenging. If Bealham takes over from Ross for Ireland and goes well, he could challenge. Francis isn't good enough IMO.
Lock:
Arguably the most competitive position in the squad. For me, Itoje and Jones are the certainties, then it really depends on whether there are 5 or 6 in the squad. Launchbury, Kruis, Henderson and Gray are the next four for me. If it's only five, it would be a very tough call, but I'd probably lose Jonny Gray. Charteris and Lawes are probably next in line, then Toner and Ritchie Gray could make a case, but I think it's hard to look beyond the top 5/6. I've also seen people mention Dillane as a possible bolter, but with so many, excellent, experienced options to choose from, I don't see it as even a remote possibility.
Flanker:
Probably the toughest to call. I'd say there are lots of players with legitimate cases for selection but no-one that should be an automatic pick. For example, if the squad had been picked in July, Robshaw and Haskell would have been in it, but if O'Mahony and O'Brien are fit and in form, I'd argue that they're superior players.
For me, the options at 6 are either work-horses or carriers. If Gatland wants a hard-working 6, O'Mahony IMO offers the best combination of work-rate, aggression and some carrying ability. For pure work-rate/defensive capability, Robshaw has to be considered, as does Lydiate (who we all know is a Gatland favourite).
If he wants more of a carrying 6, the options are quite different. Stander would be an obvious option (who can also cover 8) and after his performances in NZ, I think Moriarty has forced himself in to the Wales side and I think he's a genuine contender. Who knows how Hughes and/or Williams will go for England? If either comes through and pushes their way in to the England side, they could be wild card options.
At 7, it's equally tough. Warburton has massive credit in the bank with Gatland, but I don't think he's been anywhere near as effective as a fetcher in the past couple of years, so I think he needs a big season to be first-choice IMO. If O'Brien is able to find fitness and form, he'd be my first choice as he offers the best all-round game. If Haskell is in the same form as he was on the Australia tour, he'll be hard to overlook for the squad. Depending on how he performs with Scotland, John Hardie is also a good option - particularly given the insight he'll have in to how the breakdown is contested/refereed in NZ. Tipuric is the wild-card/game changer for me. He's a very different option to the other flankers in Lions contention and personally, I'd take him as an impact sub. Beyond that, I don't think there are any other realistic contenders/wildcards?
Number 8
One of the easiest picks IMO. I think it's fair to say that Faletau and Billy Vunipola are pretty-much guaranteed to go. Faletau is first choice for me, partially because I think he has the stronger, all-round game and partially because with Webb a likely starter at Scrum Half, I think the 8/9 combination is key. I also think Billy is arguably better used as an impact sub for the Lions.
After those two, Heaslip and Denton could make a case, but I don't see a third 8 going and if Stander, Moriarty or Hughes are picked, they can cover 6 and 8.
Scrum Half
Webb, Murray and Youngs are the most likely. I think the main question is who starts out of Webb or Murray. I think it’s fair to say that Webb is the better attacking Scrum Half â€" he’s certainly more dangerous from a sniping perspective, whereas Murray arguably has the better pass/kicking game. Personally, I’d start with Webb and look at Murray as the guy to close out the game.
Considering that Youngs is unlikely to start, there is a case for Care as arguably the better impact option. Potentially Gareth Davies has a similar case for inclusion? I also wouldn’t entirely rule Laidlaw out as a possible mid-week captain, but to be honest, I think he’s fourth choice at best.
Fly Half
This will probably be the most controversial area of selection IMO.
For me, Ford is the most talented of the available options with the best attacking game and a good tactical game kicking from hand. Admittedly, his place-kicking is not in the class of Farrell or Biggar’s, but with options like Halfpenny available, I don’t think this is a deal-breaker. With good performances in the AIs and the Six Nations, I think Ford could make a very strong case to start. Particularly when you consider he will get significantly better service from Webb or Murray than he does from Youngs.
Farrell’s strengths and weaknesses are well documented. Nothing has changed, but the pros massively outweigh the cons for me and he has to go.
Sexton is an odd one. I think injuries have taken their toll and I don’t think his form over the past couple of years warrants him being the automatic selection most seem to regard him as. If there are no fitness doubts, I think he’s too good not to take, but I’d want to see a big upturn in his performance over the next 12 months.
Biggar also divides opinion. Undoubtedly he has an excellent boot, but I think it’s fair to say that he hasn’t consistently managed to get the Wales back line operating as well it might have. Assuming there are only 2 or 3 spots for the 10 shirt, I think he loses out.
Finn Russell and Paddy Jackson both have something to offer, but I can’t see them getting in ahead of Ford, Farrell, Sexton or Biggar.
Centre
Another, highly competitive position. I think the certainties are probably Joseph and Davies, which probably takes care of the 13 shirt. Payne could state a decent case and his ability to cover 15 is definitely useful. However, I don’t think he’s strong enough in attack to really challenge Joseph or Davies as a try-scoring threat. Similarly, Bennett could be in contention, but I think he’d have to significantly out-perform the others to leapfrog them which I don’t think is likely.
The 12 shirt is much more open. Personally, I think Jamie Roberts is past his best. A lot will depend upon Tuilagi’s fitness and if/how he performs as a 12 for England. If he’s fit and can make a success of playing at 12, I think he can do a similar job to Roberts, but with more destructive potential.
As far as I understand, Leinster have signed Henshaw as a 13, but he’s seen plenty of game time at 12 for Ireland and I think he also offers more than Roberts.
While I know it won’t be a popular option, if England continue with the 10/12 axis of Ford and Farrell and keep winning, I think it’s impossible to dismiss as a Lions combination. Even more so if it improves.
Duncan Taylor is a very solid option who can cover 12 and 13 and is strong in both defence and attack. I certainly wouldn’t be unhappy to see him in the squad, but I’m not sure he stands out enough to be picked ahead of bigger names.
Beyond that, it’s wildcard territory. Stuart Olding looked decent on Ireland’s SA tour and if he can build upon that, he offers an interesting option as more of a playmaker than the other possible 12s. If Scott Williams can dislodge Roberts, he could state a decent case â€" particularly as he can cover 12 and 13. Lastly, I don’t necessarily see it happening, but if Ben Te’o rips up the AP with Worcester and forces his way in to the England side, he could be in the mix.
Wing
For me, North and Watson stand-out as the two most likely options. After those two, I’d actually rather play Williams on the wing rather than the next best specialist wingers.
Wing isn’t a stellar position for the Lions contributors and after North and Watson, there’s not a huge amount to choose between the other contenders IMO.
If Jonny May can find his pre-World Cup form, he has to be a strong contender and then the other possibles are probably, Nowell and Seymour.
It’s possibly a touch harsh but, Maitland, Visser, Trimble, Earls, Zebo, James and Amos are all a bit of a step down for me and unless Cuthbert re-finds some kind of form, he’s not even in the conversation.
As a wildcard, Wade would be an outside shout. If he’s ripping it up in the AP and Europe with Wasps, Gatland could be tempted and he did call him up as a reserve in Australia … then again he also called-up Billy Twelvetrees …
Fullback
This one is pretty easy IMO. It’s hard to look beyond Hogg, Halfpenny and Williams.
Brown and Payne could also be in with a reasonable shout, but after that I’d say it’s a pretty closed shop.