I have 24", 26" and 28" barrels for my Nova. I shoot all of them periodically. The best choke that I've found for that gun, regardless of the barrel length, is the SSX with a .643 exit diameter. It is however all about the "internal geometry" of the choke and I just can't find one better. You can take a look at the SSX at http://www.allaboutshooting.com
I'd also recommend the 3" Hevi-13 "Bronze" shells with 2 oz. of #6 shot. It just patterns better and has plenty of retained energy to cleanly kill a turkey at any reasonable range.
I hope that helps some.