40T is a good all around gear, if you have lots of hills a 44T may be a better choice depending on how steep and long the hills are, I use 36T or smaller on all my bikes, I weigh 215lbs and have some small not to steep hills I ride and mine all pull me just fine, as bill2781 has mentioned, it really depends on if you need speed for riding in area with small short hills or you need pulling power for steep hills and are not as interested in high cruise speeds.