Sceptile, Swellow, Medicham, Milotic, Torkoal and the sixth rotated alot.
I got Sceptile because when my friends and I got the 3rd gen games, we all decided to use a different starter. So we played rock, paper, scissors, and being the horrible rps player I am, I lost. So they got first choice and left me with Treecko. Over time I've grown to love Sceptile, and now he's one of my favorite pokemon.
Swellow was because I thought Tailow was adorable, and I usually try to get a good Flying pokemon as early as I can.
I got Medicham because the Fighting/Psychic type combo seemed really cool. It ended up he was a vaulable asset with Pure Power.
I went looking for Feebas because I needed a good Water-type, and the other new ones were already being used by my friends. So I went a fished on Rt119, and was extremely lucky because the first square I tried had Feebas.
I got Torkoal to round off my team with a Fire-type. Not to mention he's the cutest little thing.