I've been playing since Red, so I have forgotten most of my early teams, aside from key members: Charizard (my very first pokemon--from Red), Gengar (Red), Pigeot (Red), Farfetched (second red playthrough) Typlosion (Gold), Vileplume (Gold), Feraligator (Crystal), and Suicune (Crystal).
The first team I remember well was my Ruby team: Blazekin, Gardevoir (nicknamed Grazon), Exploud, Flygon, Swellow, and Sharpedo. Probably not my best team, but they were memorable enough since they were my last team for years.
When I picked up Black 2 a few years ago and got back into Pokemon: Samarout, Gardevoir (technically hacked in as a Ralts since I was playing on an emulator), Altaria, Lucario, Zorua, Ampharos, Arcanine, Gigalith, Flygon, Lopunny, and Maractus. This was the first time I actually used a rotating team, instead of beserk charging everything with 6 like I did as a kid. Probably my favorite team, all-around.
Reborn has quite a rotating in-game team: Greninja, Eelecktorss, Zebrastrika, Noivern, Swalot, Rosarade, Pangoro, Meostic (F), Lopunny, Mismangus, Spiritomb, Pyroar (F), Camerupt, Houndour, Arcanine, Chandelere, Poliswine, Gardevoir (Grazon), Sylveon, Venusaur, Metagross, Hauwlucha and Mightiana (probably off rotation next episode). A mix of everything I've wanted to use, but which Gamefreak denied me because of not having an all in one game (like Blaze Black 2)
(Horoable mentions to Krickatune (MVP of the first two gyms), Blitzle (temporary member off rotation), Lunatone (temp member off rotation), Volkarona (Mommy Larvey, currently egg hatcher; now that I had the time to evolve her, might be on rotation next episode))