I'd have to take the 30-30 over the 12 ga. in this situation. The 30-30 is a great brush gun b/c of it's small size and ease of handling. That's what I take when I go into the thick stuff and shots are the same range.

If you were sure of your accuracy w/ the 12 though, and shots weren't going to be longer than what you're used to shooting, it's hard to beat a 12 ga. slug and I might take that instead.