OK, here is the question & some assumptions.
Assuming:
1. Ron Paul is not viable or gets anywhere near the nomination.
2. Newt does not have a third life this political season and continues his pseudo-intellectual self-immolation for the entertainment for those willing to parrot, "Newt is really smart, but..."
3. The GOP nominee must, eventually make nice with the Tea Party-ish elements in the GOP to get the nomination.
Who is the better pick: Romney or Santorum?
I could go on & on about how both are inadequate and not to my tastes. Most of them are equally bad on many, many issues, so it sort of cancels those issues out.
Trying to look on the upside, I think, hold on, <cough-retch-shudder> that the better of the two is probably Santorum.
Santorum has actually governed and defended conservative positions while in elective office. He's won more than one political race. He has never run to the left of Teddy Kennedy. He can speak conservative-ese. (Romney speaks conservative-ese like it is a second language.) He might be bright enough to understand that just like the GOP isn't going anywhere if it jettisons the social conservatives, the social conservatives aren't going anywhere without the fiscally and constitutional conservatives.
Given a Tea-Party-tinged Congress, Santorum might be the better choice.
To be fair, Romney has the following going for him:
Great hair.
Successful business leader.
Beau coup campaign money.
Snappy dresser.
Great hair.
Of course, neither is yet willing to face the true gravity of the financial situation and propose action like Ron Paul has. Ron Paul's serious flaws (foreign piolicy, illegal immigration(1), insufficient sensitivity to Aggrieved Groups back in the 1980s & 1990s, etc.) sort of fade in the face of Getting the Big Question Right.
My future dream team:
Rand Paul / Allen West
(1) Sure, let in millions more welfare teat suckers and un/semi-skilled wage undercutters who will vote Democrat when amnestied (while trying to reform welfare). What could possibly go wrong? (Quoth the raven, `Nevermore California.')