Any of those will do.

My problem is that I don't want to get rid of certain characters, and the ones I did have been replaced already.

See, the common Knuckles are:

King DeDeDe - King K. Rool
Ike - Cloud
Sonic - Sonic
Lucario - Mewtwo
Pikachu - Pikachu
Luigi - Luigi

Those are the ones I saw...well anyway the left is who is being replaced and the right is what I replaced it with.

I could care less if ROB, G&W, or Wolf are in my game. Ice Climbers as well but I don't think that works.