As always I'm having a very hard time with superlatives. I cannot name one single character whose return I would welcome most of all. Having not yet seen the returns of Ali and Doc in the TV series I cannot say anything about those returns either. A good comeback of Ali would certainly be great. Pterano too is a character of great potential. Not quite as potential but still quite adequate for a return are Hyp, Nod, and Mutt, and Mr. Thicknose.
I guess may vote for the character I would not want to return is somewhat easier. While Ichty and Dill still have some interesting elements (two characters despising each other but also being dependant on each other, no clear domination in the pair of villains (certainly not as clear as in case of Ozzy and Strut), a physical disability of a villain) I don't see anything interesting introduced to the series by the character Tippy from LBT 8. As Tails quotes me in his signature, I really think he comes accross like a dinosaur shaped Teletubby! Everything from his name, to his way of talking and his strange color seem to aim in that direction. He didn't do or say anything of significance while there would have been a chance to make so much more of a character Spike could closely relate to without making that character silly. I really don't think Tippy is necessary for LBT.