Looking at a decision on voting for Romney or Obama I can't find much of a difference.
Well honestly, what did you expect? You're an identity politics voter, and Romney's never going to be able to speak the evangelical language fluently cause, y'know, Mormon. Speaking as a democrat, I would say that Romney's campaign promises make him more consevative than Dubya back in 2000. And the Republican party in its current state is likely to hold him to those promises.
You want to know what the differences are between Obama and the Mittster?
The Economy: This is obviously issue No. 1, and its where the biggest differences crop up, and get to big to treat with any justices in a paragraph or two. Suffice it to say that while Obama is sticking with the moderate Democratic approach that worked for Clinton in the 90s (but wouldn't be my preferred course of action), Mitt seems to think that the way to prosperity is to hand money, and power to the same corporations that got us into this mess, then step back and stop regulating them.
The Budget: Romney has endorsed Paul Ryan's budget that would recognizes and gives comfort to those of us who are really suffering in the recession (the military and the ultra-rich) punishes the people who don't need any government assistance (everyone else).
Healthcare: Romney has promised to do what he can to dismantle Obamacare. Of course, we don't know how he plans to do that, but considering the ACA is projected to reduce the number of uninsured by 32 million (while slightly shrinking the deficit) I'd say it's important.
Also, it's worth pointing out that Romney signed on to Ryan's plan to kill off Medicare as we know it.
Energy: Romney may grudgingly acknowledge that global warming is happening, but he doesn't seem prepared to do anything about it. Obama's EPA is finally starting to do its job after 8 years of dormancy, and Romney would kill that.
Foreign Policy: Romney seems determined to get us into a war with Iran at the nearest opportunity. He mocked Obama's succesful "lead from behind" strategy in Libya, and thinks we shoudl make the same mistakes in Syria. Like the rest of his party, Romney seems to think that the way to beat Al Qaeda is to piss off Muslims until we're fighting the entirety of Islam.
Immigration: If it passed Congress, Obama would sign the DREAM act, and Romney would veto it. Obama believes in a path to citizenship for immigrants, and Romney either doesn't or is to afraid to say so. Simple as that.
The War on Women: Romney may not be able to "shut down" Planned Parenthood, but he could certainly deny it federal funding. That would increase the number of abortions performed in the US, but whatevs. He'd re-institute the Mexico City Policy, with the same results overseas.
Judges: They say that the longest-lasting legacy of a president is the judges he leaves behind. I don't think anyone told Obama that, because the federal judiciary has an alarming number of unfilled seats, due to a combination of unprecedented Republican obstruction (not hyperbole, check out the statistics on senate holds and filibusters) and Obama's seeming disinterest. And of course, the Supreme Court is a knife's edge, with four conservatives, four liberals, and one kind of conservative moderate. The winner in 2012 is going to have a lot of impact over judicial decisions for decades to come.
In anycase, the Presidential election isn't really about electing Presidents, it's about electing Presidencies. A Santorum staffed Executive Department would have the same people as a Romney staffed Executive Department, and both would look frighteningly different from Obama's Executive Department. The differences between Candidates Santorum and Romney would be smoothed out by their essentially identical appointments.