The guys who say horse has no advantage over cow initially offered only cow. Kramer was the first to widely offer horse only. I know Mitch Rosen resisted horse for years but now offers it. There's a lot of "Professional Jealosy" amongst holstermakers. Both guys make great stuff, both cow and horse.
Horsehide is more expensive, rarer, and much harder to block or mold into shape. Cowhide does not last as long, but it will last a long time. Even if you carry daily, practice daily, it'll still last for many years. You'll probably end up getting a different gun, and thus a different holster before you wear it out. Horsehide WONT wear out, at least I haven't been able to.
My daily carry rig is a Kramer IWB (horse), on a Rosen belt (shark), with a Rosen mag pouch (cow). How's that for compromise!