longer within reason is going to divide the rotations over more feet of chain, which should increase chain life, and more room to put in a tensioner. at extreme lengths you have alot of chain slop to deal with if you dont have a way to tighten or tension.
a benefit of short, you may not need a tensioner/adjustment as long as the chain will stay in place it wont be able to twist enough to pop off.
in the end, make it fit, chain is a consumable. if you have a choice between shorter wheel base and longer chain, I would take shorter wheelbase most of the time, as this gives you a tighter turning radius. hope that helps.