Gallup Poll. Dec. 11-14, 2006. N=425 Republicans and Republican leaners nationwide. MoE ± 6.
John McCain 28% ; 26%
Rudy Giuliani 28% ; 28%
[+ others all at 2%, 1% or less]
Also, Human Events reported last month in "A Primer on the 2008 GOP Candidates":
... Mitt Romney is an interesting character. Although he is the outgoing governor of the very liberal state of Massachusetts and was named as one of the Top 10 RINOs (Republicans in Name Only) less than a year ago in HUMAN EVENTS, he's not as liberal as he might appear at first glance.... [A]ccording to recent polls, even if you set aside the debate about how conservative he is or isn't, the "Mormon issue" is starting to look like an insurmountable obstacle to his candidacy. According to Rasmussen Polling, 43% of Americans and 53% of Evangelicals say that they, "wouldn't consider voting for a Mormon candidate." For good or ill, that probably means that Romney is unelectable.