Romney has famously flipped on abortion, his political leanings, cap and trade, immigration, and (highest of treasons) health insurance mandates. In each case, he's flipped to being harder.
Santorum's flips have been less notorious. He's been walking back his opposition to homosexuality. In the past, he thought it was fine for states to criminalize homosexuality acts. Now, he'd love his son if he was gay (and suppress those lectures on unnatural sex acts, I guess). He's also flipped on raising the retirement age, auditing the Fed, teaching intelligent design as science, right-to-work laws, and No Child Left Behind. Santorum has usually flipped to being softer, except for his previous support for unions and national education initiatives.
This is an important distinction with you're a red-blooded conservative. Do you support the johnny-come-lately conservative, or the becoming-less-paleolithic conservative? Most red conservatives are going for the barely-escaped-the-paleolithic conservative.
For me, it's an easy choice. I hope that, under all his recent pandering, Romney is still a moderate. I also think he's the Republican most likely to address our deficit problems. With Santorum, I suspect it's lower on the priority list, somewhere below "Pursue expensive war on Iran."
I wonder who the whole of the Republican party, not just the hard-core conservatives, will choose. Is there room for a semi-moderate who pretends he isn't? We shall see.
Getting to be a GOP tradition...