Conventional wisdom says Romney but Thompson’s polling data points to Giuliani:

Among moderate Republicans, Thompson’s support has increased by 14 points (4% to 18%), while Giuliani’s support has decreased significantly (37% to 29%). McCain (19% to 16%) and Romney (8% to 3%) have also lost support among moderate Republicans. Giuliani shows a slight loss among conservative Republicans (25% to 22%), while Thompson (16% to 18%), McCain (14% to 16%) and Romney (8% to 10%) show slight gains.

It would be good news if Thompson could steal some moderates away from Giuliani because Giuliani has a good chance of winning this since there are way too many conservatives in this race and they are going to split the conservative vote.