i mean anything could happen, as the match would come down to just a few points.
I'd lean towards Ivo tho. The better question is what would the head-to-head be out of 10 matches. I'd say Ivo 6-4. MAYBE 7-3 depending on surface. With one match, its just too tough to call. Whoever comes up with the even-more-massive-than-usual serves at the right times.
There's absolutely no way either would break serve. Isner's 1st and 2nd serves are just insane. Ivo's 1st serves are insane and the 2nd is pretty good and he can back it up against Isner. It would come down to TBs no questions. To be honest, despite being #1 Ivo fan, I think Isner is a more clutch server in the TB. He just bombs 1st serve after 1st serve in, and even if he throws in a 2nd serve it's pretty much unreturnable. Head to head my vote is Isner 7-3. However I think Ivo will consistently do better against the rest of the competition than Isner and will maintain a significantly higher ranking through his career (which hopefully will last at least 5 more years!)
karlovic should win it. he got lot more experience.
isner got an edge on bh. 2nd serve is good but lacks agressive game. He kind of baseline player.
but karlovic got the edge on serve,volleys, forehand and agressive game.
i don't think they would meet with each other atleast until next fall.