Sawsbuck
Sawsbuck is a really cool Pokémon. I like its design, and I like the multiple forms they implemented for it. Like Helioptile and Litleo's families, the Normal typing gives them access to scary STAB moves like Hyper Voice. Can't say I've ever used it in battle, but I do in fact have a (Spring) Deerling in AlphaSapphire from White. Spring and Summer are tired for my favorite forms, but Summer takes the cake for me because it was the month I was born in. If the different forms had unique moves (and I can completely understand why they don't), here's what I'd give them:
Summer: Leaf Blade (I dunno? It already knows Solar Beam regularly, plus it's physical and works with Grass typing)
Autumn: Leaf Storm (also Grass STAB)
Winter: Blizzard
Spring: Razor Wind (cause spring is windy, also because it works with the Normal typing)
THUNDURUS
Eh...I don't have many good memories with the Weather Trio. I despised their designs when BW came out, and they still leave a bad taste in my mouth today. Yeah, they look like powerful, intimidating beasts, but they're just...ugly. Landorus and Tornadus' Therian forms look even worse. Thundurus' actually looks kinda badass. Thundurus are still waiting to be caught by me in my W file, I may go do that someday, or just get the one in AS.
Metapod
I have a kind of respect for Metapod and the other cocoon Pokémon, for their neat designs and their outright silly portrayal in Pokémon media and reputation in the fandom, and I respect it for being such a trooper. :P I haven't done a Meta v Meta before, but it sounds like it'd be pretty hilarious. While I love green and yellow together, I think light blue complements Metapod's shade of lime-green than yellow.
You go, Metapod!
Infernape
Ah, now I've some good memories with Infernape. For both Diamond and Platinum (the former of which I lost a little in between DP and Platinum came out), as always, I picked the Fire starter, Chimchar. In the latter, at least, he eventually evolved into an Infernape, and I remember him being one of my most-used Pokémon throughout the game, including in contests. Like my previous generation Blaziken, he eventually learned moves Fire Blast, Cut (I always thought my starters Cut...needless to say, I do not anymore), and Hyper Beam. I've since moved him up to my Gen 6 games. ^^
I don't really mind its typing, but it is nice to get some variation once in a while. I love its design and colors, I think the overall look of the Chimchar evolutionary line progressed quite nicely. Its got nice stats as well- equal Atk and Sp. Atk complement its Fighting and Fire typing, respectively. As for Ash's Infernape, I think I stopped frequently watching the anime a little after or before it evolved into Monferno, because I don't remember that much of it. I did like it as a Chimchar though, and I felt bad about how it was treated by Paul prior to its ownership by Ash.
Snorlax
As iconic of a Pokémon Snorlax is, I don't recall ever using him in battle. I really like him though. He's silly, he's got some darn good competitive potential, and I'll never forget his appearances in Smash Bros. and the anime. I liked the callback to the original games with having a Snorlax block the Route 7/Rivière Walk bridge in Kalos. I caught it, and haven't done anything with it yet. I'll be definitely looking forward to encountering the ones(s?) in RBY when they come out on the 3DS in a couple weeks!