You and I are going to have to agree to disagree on this one. Hitmontop, in my opinion, is much better than Donphan as an OU spinner. Donphan tries to do too much (set up Rocks, spin, kill dragons, etc.) for something that is so easily killed due to his piss-poor special defense; it's weakness to Water, Ice, and Grass type attacks; as well as its mediocre attack (when uninvested). Also, please don't even try to say that Donphan uses Odor Sleuth. Donphan's moveset is Earthquake / Stealth Rock / Ice Shard / Rapid Spin. I mean, look at this month's usage stats:
Odor Sleuth isn't even mentioned as an option. That's because, like I said, Donphan tries to do too much as it is. Adding Odor Sleuth to its moveset makes this problem even worse. Plus, Hitmontop gets great moves like Close Combat, Mach Punch, Fake Out, Bullet Punch, Sucker Punch, etc. which are all great options for taking out certain threats to your team. I still think the lack of Water/Ice/Grass weakness is enough to make him a better choice than Donphan on Sun teams.