liek i luv Arceus!!
Just kidding (Arceus is probably my least favorite)...My all time favorite is the awesome ARCANINE!!!!!!!!!!!! I love the thing, it looks so majestic. It's also a fire type which despite it's weaknesses, is my favorite type.
Some other favorites I have are Dragonite, Venusaur, Blastoise, Charizard, Typhlosion Magmar, Farfetch'd, Golduck, Kingdra, Flygon, Gyarados, Gengar, and Alazakam