Wow. Very hard question right there. Uhm.
First and foremost, I'd like to say I wouldn't want to nominate anyone who has recently stepped down from admin or mod roles. Without exception I think their resignation is somewhat a loss to the community, but if they feel they need to step away from the role, then it would be disrespectful of me to try to force them back.
A lot of people would pick forum-goers that they're friendly with for such a role, but I can't really do that - the members I feel are mature enough are, pretty much universally, either too new, inactive or are already staff. There are a few that I'd say "give them a couple of months, let them know the community better, then they'd be ready".
The obvious choices that others have jumped to seem to be the "celebrities" of the forum; even assuming they have the necessary qualities, I think choosing such a member would be a bad move. Their popularity would detract from their responsibilities, sadly.
There are a few members who have become apparent to me lately in showing a lot of enthuisasm and maturity on the forums, and I would gladly suggest them, if only I didn't feel that perhaps they were too eager. The moderation role requires not only quick thought and action, but also the wisdom to sit back and consider situations more fully.
Soooooo... after all that, sadly, I have difficulty thinking of a single current member who would be as fit for the role as any of the current staff. Sorry about that.