Out of the fish I routinely encounter, barbel, size for size, are well out in front. Another question would be which fish fight smartest, and chub would be the winners for me. Exciting as barbel fishing is, I think I prefer chub and tench. You can get them out on the kind of gear that makes a mixed catch enjoyable, there's a bit more of a battle of wits involved, they put up a good fight, but it doesn't take ages to get them in on lightish gear, so you can get back out fishing for another! It's not as if the fishing automatically gets better just because fish fight harder.