i find 2:1 way too steep for most of the crap i ride.

i rode 34x20 on a 26er and now run a 34x21 on my 29er.

the 38 with a 21 or 22 in the back is what i'd recommend unless your real strong or your trails are pretty flat.

just like fixed; you don't need to push a monster gear if you can spin well.