Oooo, that's a hard question. I really love Lois, (yes, who wouldn't want to be married to Superman) but I love *watching* her interact with Clark and watching their love story. So I'd probably want to play someone else who is good friends with the couple.
I'd want to play a female character though, and not an old one. So I dunno, maybe Penny? Jimmy's season 4 girlfriend. The FoLC's ended up having her and Jimmy get engaged in Season 6. So that wouldn't be bad, being married to a sweet guy like Jimmy. And you'd get to hang around with Lois and Clark a lot.
Not to mention Penny stole a kiss from Superman. Tee hee.
