These aren't in any particular order because I'm super indecisive (except Pidgeot, he'll always be my #1 fav)
1. Pidgeot. Just because it looks like a cockatiel. :3
2. Vaporeon/Sylveon. Used to be Umbreon, but Umbreon doesn't suit my battling style. I just really like how tank-y Vaporeon is, and Sylveon is surprisingly strong.
3. Lugia. Especially Shadow Lugia. I've sadly never actually played Pokemon XD: Gale of Darkness, but Shadow Lugia just looks so cool and strong...
4. Flygon. I love this little guy. I feel so sorry for him though, since he didn't get a Mega and is almost always overshadowed by Garchomp.
5. Rowlet line. Rowlet's just soooo adorable! And his final evolution is just so... ahhhhhh! > u < The shinies look the coolest too.
6. Giratina Origin Forme. I don't need to explain this.
7. Ralts line, especially Gallade. Gallade was one of my friends' favorites. I haven't heard from him in years, but I still really like these Pokemon because of him. -///-
8. Empoleon. First starter I've ever chosen, so it has a special place in my heart, of course.
9. Samurott/Emboar. I liked Samurott because Oshawott was cute, and Samurott was awesome. I didn't like the Tepig line at first, but after trying it out, I love them.
10. Mega Blaziken/Charizard. Both are really overrated and OP, but they're still cool. It's especially fun using Bulk Up or Power-Up Punch with Mega Blaziken. Heightened Speed, Attack and Defense. > v <