The best candidate I think is John Edwards. Firstly, he is from the South, and even if he does not win a single Southern state except North Carolina and maybe Missouri, that is 15-26 electoral votes right there. Certainly more than Dean, Lieberman, or Kerry can bring to the table.
He's hurt by running for President mid-way through his first term in the Senate. I recently saw a poll from NC that showed Edwards losing to Bush in NC 49-42%. Nobody knows who he really is. It'll be Dean vs. Gephart down the stretch. Will the anti-war types flock to the Green Party if Dean loses the nomimation?
Actually if Edwards is trailing Bush 49-42 it usually means he would win the state about 49-50, because Bush is the incumbent and about 75% of undecideds vote against the incumbent.
So I doubt it's worrying him a lot.
Anti-war types will flock to the Greens no matter what happens, Dean's Battle Flag remark and refusal to call for an immediate pull out from Iraq has really pissed them off.
But he doesn't need 'em now anyways.