Honestly not enough difference to matter. If it will be used mostly for tasks like bird hunting, clay targets and the like I'd go with 26" but that 2" just really doesn't matter.
For doubles I prefer 28" as the action is so short it helps balance the gun better for me but with pumps and semiautos the long action makes a 26" barrel gun as long or longer than a 28" double.
For trap shooting, pass shooting and the like I tend to go with longer barrels (30" or more) but for most else I tend to pick 26" for repeaters. Try to find both in a store and see which feels best to you that's the one to go with.