I like both. Dunsparce likes to troll a la parahax, while Mawile is just adorable. (I also thought Mawile was Dark when I first played Sapphire because of the moveset and looks. Seriously how is it a Steel type? But I digress.)
My vote goes to Mawile, for several reasons. First, Mawile is adorable (seriously, those teeth are beautiful). Second, Dunsparce is, like Spinda, a mostly pointless Pokemon (who I wish would finally get evos) Third, despite Mawile's stats being rather meh, I actually found her fun to use in game.