I am on Sinnoh in my normal ultimate, so let me pass on what I learned:
1. For the last three Gens, Return is a beast. Get as many as you can!!!
2. Gen I - Clefable, Raticate are both good (i'm not so hot on Wigglytuff), and Doduo is the best bird type overall.
3. Gen II - If you use Crystal, Clefable is in there. If not, use Girafarig (G/S). Pidgeot is your best flying option, and I also used Furret. Miltank or Tauros are both beasts and can learn EQ, though I used Miltank, and she was my savior against Lance with Rollout.
4. Gen III - Swellow is your flyer. Exploud for special, Zangoose is uber with Swords Dance, and Linoone can be useful if you want to use him (I didn't). Slaking can't learn Skill Swap, so no getting rid of Truant, though he is a beast with Return and Earthquake.
5. Gen IV - Lots of options here. I would go with Platinum so you can get Togekiss - Air Slash is epic with Serene Grace ability. It can take patience to train, but it's worth it, and Togetic isn't horrible. Staraptor is a good option as always. Girafarig, Lickilicky, Porygon-Z (trade evos or Pokesav for emulator), Clefable, Lopunny, etc.
wow that was longer than I thought it was gonna be. Just remember, RETURN!!!