It would have to be a tie between LeBlanc and Diana. I love LeBlanc's playstyle the most by far (the whole "I'm here! Now I'm here! Now you're dead!" thing), but I find Diana really insteresting (her voice, her design, etc).

Special mention to Karma, whom I absolutely love everything about but the fact that she's useless... Seriously, her voice acting is the best in the League by far.

Orianna. She's a haunting creature that's extremely intriguing to play, and look at.

LeBlanc just because of her burst
http://www.youtube.com/watch?v=cmqboECd79o&feature=plcp

I really had a hard time deciding who's my favorite champion.......Then Ziggs went on sale.

Hecarim

His mysterious origin kept me intrigued. And now the "Remember who you once were, Hecarim!" from Twisted Treeline, Hecarim definitely has some interesting lore coming.

1st: Diana (Moon is pretty cool )
2nd: Elise (Shapeshifting into a terrifying Spider? Yes please!)
3rd: Pantheon (Thighs...nuff said)
4th: Syndra (I like the orbs rotating around her...)
5th: Zyra (Using nature to fight has always been cool for me)

Sion
Don't laugh

Malzahar. He has a cult of void worshipers and I love spreading his space aids around (malefic visions). I also like the ridiculous damage output of spreading crabs (voidlings). LOL yea, 4:30 in the morning. Definitely inebriated. GG

Too many to name them all but LOVE
-Ziggs,
-Nautilus
- Ahri
- Kog'maw
- Dr. Mundo
- Amumu
- Vladimir
- Zyra
- Yorick
-Renekton