Either one will work just as good as the other. Just remember that if you use an extended choke, like the Jelly Head for example, you'll be adding 2 inches to the over all length of the barrel. If that's the case, I'd get the 20" barrel and go with a 2" extended choke and you'd have a 22" barrel. Likewise, with the 24" barrel you'd have the 2" extended choke and effectively have a 26" barrel.