I`ve got one of each (sigh). But the chestnut mare (aside from the occasional very mild tantrum) is way nicer. When she tries to pull something, I tell her don`t you try that on me, the $/%$" gelding has already taught me how to deal with that in spades.
He is so cute, congrats! He looks like my pony's best friend. Mr. Pony himself is also a total @$$, but he's a pony. And chestnut. And also a burnt-out former lesson horse. We start every ride with "SCREW YOU, MOM" but then he gets over himself and I have my fabulous little dressage horse, jumper, and trail buddy for the rest of the time. :) He's a super grouch on the crossties, and is a jerk to other horses, but once in a while the softie in him comes out and he'll just snuggle and hang out with me, and come with me on my hair-brained adventures. I don't think I could own a horse without a personality quirk! Too boring. ;)