42t Cog, love it!
I have been running the 42t cog on my DiamondBack Mason for 9 months, it has worked flawlessly, and Im able to climb some trails that were a bit unapproachable on a 36t previously :)
I have a 1x10 set up, SRAM parts, 30t RaceFace chainring. Excellent trail/all mountain riding set up.