As an old school Pokemon fan I'm going with the king from the original 150/151:
Pidgeot!
Pidgey was the first one I ever caught in pokemon blue and was my go to pokemon for nearly every difficult battle.
My favorite is Reshiram,from Black.1:He looks plain epic 2:i really like the concept of it. The White ying Pokemon,who is the master of nature,and fire.3:I love how it was desighned.Fire comes out of his tail,which is sorta like the source.He looks like flaming white fire,with his wings and the back of his head.
1st generation ftw.
There's too many I have to choose from, so I'll list'em off
Alakazam
Mr. Mime
Kabutops
Dragonite
Gengar
Pinsir
Porygon
Charizard
Blastoise
Hitmonlee
Muk
Gyarados
Aeodactyl
Magmar
Electabuzz
Kanghaskhan
Chansey
Tauros
Lapras
Magneton
and Golem
If I had to play favorites, I'd choose... Muk, because I had him nearly sweep Lance (if it weren't for Aerodactyl's speed) in Pokemon Silver. Not to mention he's a pile of sludge with an arm that can discharge electricity, ignite, or freeze solid. Also, Toxic.
I'm gonna be, the very best. Like no one ever was. To catch them is my real task, to train them is my cause. I will travel, across the land, searching far and wide. Each Pokemon, to understand, the power that's inside.
Hehe. Anyway...
My favorite Pokemon is probably Vaporeon. Mew would be second. He's second rather than first only because I couldn't get him in the game.
Jigglypuff! She's so awesome, and her health skyrockets in the games like nobody's business. I had a demon Jigglypuff in Red that knew Mega Kick, Psychic, Thunder, and Blizzard. I could take out the Elite Four and Gary with her alone. Plus, I totally own with Jigglypuff in SSBB.
Well, I'll name my top three from each gen and then tell you the winner.
Gen.1: Rapidash, Clefable, Pidgeot
Gen.2: Ampharos, Aipom, Heracross
Gen.3: Sceptile, Salamence, Blaziken
Gen.4: Mamoswine, Lucario, Magmortar
Gen.5: Shimama, Emonga, Tabunne
I'll do mine from each gen as well.
Gen.1: Pikachu, Charmander, Pideotto, Mew
Gen.2: Cyndaquil, Totodile, and Chikorita. (A.K.A the starters)
Gen.3: Mudkip, Rayquaza, Salamence
Gen.4: Turtwig, Luxray, Rioulu, Arceus, Dialga, Shaymin
Gen.5: Pokabu and Zekrom