With Biggar's game management, kicking, and defence being far superior to that of Priestland's, it's difficult to understand why Gatland favours Priestland in the first place for the conservative game plan he has Wales playing at the moment. That's before factoring in Priestlands dire form since the 2011 world cup. Priestland can be a creative player, but only when he's confident, and there's been precious little evidence of any sort of confidence in recent years, for either Wales or the Scarlets. Injury might not of helped, but he was poor before his big injury too.
If Gatland wants more from his 10 than what he thinks Biggar offers (I think Biggar does offer something in attack personally), then questions should be asked about why Hook hasn't been given time playing at 10. I do think Hook has been a bit meh in his cameos off the bench at 10 over recent years, but Priestland has been worse, yet given chance after chance. There's a lot of double standards going-on, and I'm sure the likes of Hook are well and truly fed-up with it really.
The Welsh management have voiced their admiration for Patchell in the past, but he's currently out with a serious injury, so he's not currently an option. Regarding TheSaffycen's comment about his kicking, he's got quite a boot on him, great distance. But that hasn't helped Biggar's cause, who imo is a world class place kicker. With Halfpenny out though, it'll likely increase his chances of starting ahead of Priestland on the summer tour.
I've not had a chance to see Owen Williams play since his move to Leicester, but I've hears good things. Still a little early for him though I feel, as 10 is a position where a player can't be rushed imo.