Again I am in a guild with 27 normal raiders and not one of us enjoys 25 mans. Even though out of the 27 that normally raid, 27 of us are all competent, know our roles and would not have to worry about each other messing up if we were in 25s. The only time we do run 25s, is when we have Heroics on farm and we have some of the alternates who might be lagging behind with gear. Not once after any of those 25 man runs had anyone ever said we should run 25s as a guild.
We run 10s because we love running 10s.