Out of the options available, Giuliani has proven himself to be a strong leader in crisis and peerless on law & order issues (a good sign for constitutionalist judges and military issues).
As a result, he's my pick at this very early juncture. Besides, a president has next to zero impact on any social issues (how much movement have Reagan, Bush I and Bush II brought on abortion?).
Due to the dynamics of the race, Romney is smart by attempting to co-opt the religious right. Still, they are the one group most resistant to the LDS. And the more he poses as the religious conservative, the more objections he'll get from the secularists to his LDS background. A dicey game.
The Daily Rudy
Having to duke it out with Freepers every day about Giuliani for the next year and a half is going to get old real fast. At this moment, Rudy's my choice. Right now our strategy and vision on the War on Terror is sucking wind, and we’re on a path where the nation may just give up the fight. Giuliani’s the only one who can refocus and rally the nation again. IMHO, the WOT trumps everything else.
How can Romney be considered a social liberal when he's been married to the same woman for 37 years, vetoed the stem cell bill, says he is pro-life and opposes gay marriage? Perhaps he could be seen as socially moderate in some people's eyes, but he is no social liberal. Even these guys don't think so, see Here
Bush II put two likely votes against Roe on the court. Id say he made an impact on social issues.