I don't think the opposition will be losing too much sleep over whichever of them starts. The main interest will be whether or not the Lions expect their 10 to be a part of this 'rush' defence, flying up to put pressure on BB. In my view, that would be suicide. A little sidestep, a quick shuffle and you're looking at 7 pts. Nobody is catching the boy. Or a quick crossfield kick to the wing (to which he's partial, and rather good) and, again, it's try time. TBH, the only way to deal with him is to a) make sure that he rarely sees the ball (difficult), or (b) to have someone equally as good (they haven't).
I suspect that Gatland will attempt to go for the former. Starve the ABs of decent possession, and hope that he only gets the ball in pressure situations. That won't work though. If the AB pack is at full strength, then nobody is going to get much better than parity against them. Read, Kaino and Coles are important players to have fit for the ABs in that respect. And they could do without losing Retallick or Whitelock, as well. We saw how the physicality of Ireland upset the ABs in Chicago, when they were missing the latter two, and Romano had to go home, with Kaino playing at lock (!!!). I don't think we'll see Kaino at lock again. Just a guess.