I'd have to say that my top ten would be something like this:
10: Sableye. As a Kingdom Hearts fan, Sableye quickly became a favorite of mine for it's resemblance to Shadows
9: Zangoose. I love it's white and red scheme and overall design, plus just how menacing it looks.
8: Mega Absol. The whole angel/unicorn motif for me just sold me on it, though I liked Absol before mind you.
7: Gallade. I like Gardevoir, but Gallade just looks so much cooler... maybe it's the fact that it resembles Adam Jensen.
6: Grovyle. This largly in part to Explorers of Sky, but I've come to like Grovyle a lot better than Sceptile
5: Blaziken. Fucking. Flaming. Chicken. Martial Artist.
4: Rayquaza. Is it just me, or am I a massive Gen III fanboy? BTW: Best shiny ever.
3: Ampharos. Not quite sure why, but ever since HG/SS, I've just liked Ampharos's design.
2: Typhlosion. Hands down my favourite starter ever, it's basically a walking napalm factory that looks both menacing and adorable at the same time.
1: Lucario/Riolu. I honestly have no idea which one I like more. Both of them have great designs, and their use of aura makes them even more badass... it's too bad GF has to make everyone who likes them look like rabid fanboys by shoehorning them EVERYWHERE,