Romney.
Now, If only he were running.
I doubt that Romney would be aggressively anti-illegal immigration, but it is a moot point. Romney did deny in-state tuition to illegals, but that was largely regarded as a political move in anticipation of his running for president. His only other intersection with illegal immigration as governor was his hiring (unbeknownst to him, he says) a company that employed illegals to do his landscaping.
Nowadays Romney talks a good game on immigration, and if one is inclined to believe what politicians say, then I guess he would be tougher than most of the top candidates. Given his ties to Wall Street and big business, I have my doubts that Romney is a true believer against any sort of amnesty.
My main objection to Romney is the same as it is against Bush: he cannot win a general election.