Both of those look like good bikes.
I tried 27.5 and bought a 29r
I ride on the street to get to dirt roads, and the 29r does this better.
If you are strictly riding dirt and single track, get the 27.5.
I ride mild single track with the 29r.
It's your chioice... can you go to a bike shop and test ride a 29r and a 27.5, even if they aren't the bike you want to buy?