Haunter - It's definitely looking cooler and scarier than Gengar, although Gengar isn't bad, either.
Rhyhorn - Okay, when I first saw Rhyperior I was really disappointed. That hasn't changed to this day. How can an awesomely cool Rhyhorn turn into a fat, armored.... thing apparently wearing a bullet-proof west?
Dragonair - I like how Dragonite looks, like that goofy, careless dragon, and I love having it in my team. It's just that Dragonair has that beautiful, elegant appearance that can't br replaced that easily.
Grovyle - Definitely cooler than Sceptile. I've never really liked Sceptile at all :\
That's about all I can remember at the moment xD