Oh please don't do the "List of pokemon with pictures, no explanations and no credit to sources... It is annoying and spam. So is the "okemon name" variant... Or "list of names"...
All time favourite will probably always be Lugia. The second movie kinda did it. Big guardian of the sea, strong, but up against too much. Living in the sea, and his theme is rather nice too. All in all a pleasant experience. Otherwise I generally stick to fire pokemon. Because fire is awesome, as most people will point out, it is a rather exclusive group, and it contains a lot of my other favourite pokemon from the first two generations.
Other honourable mentions are the eeveelutions for being so diverse and yet so similar. Besides they kinda talk to my collectors' urge. Most starters, though mainly from the first two generations, because those were what I grew up with, they evolve into badasses and that is just how it should be.
My all time favorite will probably always be Espeon, mainly for how amazing he looks like and his stat build. Aside from that, there're a few to point out, but no specific groups like starters and legendaries, because there always come exception amidst them, i.e. the regi trio, emboar and infernape, etc.
Victreebel, Arcanine, Luxray, most of the insect types of the last gen; hey, Scolipede and Galvantula are just over-the-top cool, anyhow, I could go on like this a good while. You know, with about 700 of the criters, choosing a favorite is rather hard, that's why my choice is based on an impulse rather than a though decision.
And first that came to mind is my cute little espeon ^^.
My favorite is Dunsparce!! Gotta love beating 2 of Lance's Dragonites with para-flinch!! Other than that, Ambipom. I love fast with Technician and U-turn. Also, the episode where it played Ping Pong was awesome.
After diamond versions (Wich i lost, dont know how) i kinda disconected from pokemon world... So i dunno many of this new pokemons that camne out... Anyway, my fave pokemon is ivysaur
My all time faves from the first Generation would have to be Bulbasaur and his Evolutions, Gastly, and Arcanine were cool, and I liked Hypno alot as well. I would say Charizard but it's too cliche. Other ones from other series are Houndoom and Sneasel, they were great. Kirlia and his Evolutions as well as Bagon and his too, were cool. Absol was awesome and Sharpedo was cool too even if he was weak. Any of the Gen's after that I never really played much of so I can't say.
My favorite would have to be Scizor. Had to beat the fact that it's based off of a ninja and if trained right can have massive attack.
Some of my other favorites are: Gallade Garchomp Typhlosion Hariyama Alakazam Rayquaza Gengar Froslass Slaking (only in double battles with an Alakazam) Now, if I had to go by generation: 1st Gen=Gengar 2nd Gen=Scizor 3rd Gen=Rayquaza 4th Gen=Froslass 5th Gen=Haven't had much experience with it yet, but probably Serperior
