Blissey- I'm going to be using this on basically any team I have. I'm not going to tell you anything about it, but let's just say of all pokemon, it was the one I worked the hardest to get.
Primeape: I developed a love for this during my countless attempts at beating firered (to this day I'm too lazy to beat it.) I have countless ones, but my favorite is used both ingame and online (with perfect Iv's of course)
Donphan: I developed a liking when I grew one up from a phanpy in emerald. Since then, it's proven to be a pokemon you should definitely be afraid of if you ever fight me.
Wobbuffett: I like this guy, because unlike what others say, it still does the job. It might not survive for more than two or (with luck) three pokemon, but it does a great job of destroying teams.
Also, I like some things that may seem unconventional, as none of them are powerful. But I do. So here they are:
pikachu: currently in my firered playthrough. It's actually pretty good, and I used it through the entire game.
clefairy: I always thought clefairy looked way better than clefable, because it does. It also resides in my firered game.
charizard: transfered to dp, this guy was overleveled when I used him. so, yeah, I learned a lot about using only a charizard, which let to the hilarious circumstance of my ratata evolving during koga's gym. Yes. Koga's. I only had that on my team, and I think a pidgey. I have no idea where the raticate went, but I really don't care.
Oh, and I'll try to shoe in something cutesy, like cinccino or something. I'm also working on getting imposter ditto, so you might want to set up your substitutes and whip out your zorarks now. That's all.