I prefer 50 yards. If you zero at 25 yards you'll hit high out to about 300 yards where the bullet once again crosses your point of aim. A 50 yard zero lets you aim at your target where you want to hit, instead of aiming low at 50, lower at 100, real low at 150, etc.
As an 11b, I had to zero at 25 meters with my M16 and did the same with my AR's for several years after I got out of the Army. After trying LTC. Chuck Santose's IBZ I'll never go back to 25 meters.