all personal preference. 28" barrels usually pattern easier and hold velocity better but are more of a pain in the woods trying to walk around and maneuver. IMO 24" is the sweet spot as far as patterning and ease of use in tight spaces. I know some guys that really like the 18"-21" though but depending on the gun you want those may not be options and TO ME they are to short for my liking.
its all personal preference, velocity is all mehh to kill turkeys at 50 yards or less. ive never had a shotgun barrel I couldn't get to pattern with a variety of chokes and loads no matter if it was 28 or 18 inches, just takes a little homework.