Hm... I would have to say either Braviary, Chandelure, or Tornadus Theiran forme for my favorite Gen V Pokemon. Although I LOVE Sawsbuck, Ferrothorn Pidove (I have no good reason), Gigalith, and Serperior with so many close ones. I really like Gen V, contrary to what I see (many people I see just loathe this gen). There's many more I love, and I kept adding, but I think there's tons of great new designs.
I don't think I really hate much from this gen, to be honest. Alomolomola (sp?) is a pointless and easily forgotten Pokemon. I wish they kept it as the rumored Luvdisc evolution. Damirtan or however you spell it just seems... off to me. Like it's Infernape and Heatran put together. Semipour creeps me out a bit, too. This legendary trio is my least favorite so far, and Klang is unappealing to me. I like Kling, and Kling Klang, just not Klang.
I hate Sunfisk because it's purposely meant to look stupid and it's my only Gen V shiny. I never minded it until one day I was EV training and encountered a shiny one. Like really, out of all the shiny Pokemon I could get, I get the one that is purposely designed to look like an idiot. xD