It's a close one between Roscoe and Elmer. You've got Roscoe, on one hand, who's tall, dark, and handsome; but on the other hand, you've got Elmer, who's comical AND has a sweet side. Unfortunately, though, I haven't had either of them in ACNL yet. :'(
What can I say? I guess I have a thing for horses (if I said that out loud, I can name a hundred people that would never speak to me again).
It says a heck of a lot about me that my answer would have to be Limberg.
"He's just so GRUMPY!" *swoons*
Seriously, though, he's adorably gruff, and his character design is reminiscent of the sort of grouch that I prefer to date. (Needless to say I'm not a fan of the nerfed grumpy personalities - that's one thing that Wild World had right.)