Largely a matter of personal taste and there's a wide range of opinion, so you really need to decide for yourself. Forget the velocity difference and concentrate on how it handles. Try to spend a little time with various lengths before you decide what you like best. You're the one that has to be happy with it.

To me, 24" barrels might be OK on a lightweight small bore double, but not on a medium or large bore. I can't see any need for anything shorter than 26". I've never shot a medium or large bore double with 24" or shorter barrels that would have been even marginally acceptable to me handling wise.
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