You have not mentioned your political preference, which is probably a good thing. If I were you, I'd keep that to myself and hear what others have to say about the field.
In my opinion, there are only two possibilities: Barack Obama, the incumbent candidate, and one of the nine Republican challengers. If you lean American Left, the choice is easy enough. If you lean American Right, it becomes more about which candidate you feel is the most honest. (I specify American Left/Right because the two terms mean different things outside the U.S.)
Now, there are many, many reasons to choose any single candidate, ranging from the simplistic -- skin color, gender, faith, age, etc. -- to the complex and pointless: "Candidate A, what is your position on the use of fluoride in drinking water and do you think it is a possible contributor to Global Climate Change?" The answer from Ron Paul will be vastly different from that of Jon Huntsman.
One of the things I would urge you to do is become as informed about the person behind the candidacy as possible. We know them all as public figures, and more about some than others. For example, we know that Mitt Romney has a contentious history with the American Right, considering his RomneyCare plan in Massachusetts, but he was considered the frontrunner based entirely on his business skills in 2008 before John McCain won the field. We know that Herman Cain is an extremely successful businessman, but now he is under fire for unconfirmed sexual harassment during his career... and we have to wait with bated breath to find out if the allegations are true or not; if they are, he will likely be cast aside. And we all know that Michelle Bachmann is a darling of the Tea Party for her outspoken views on Conservatism, but only people on the American Right seem to know that she also raised 23 foster children.
These are the sorts of things I would focus on, at least until we start to lose candidates and narrow the field. We all know about the hot-button issues -- no one will shut up about them! Instead, see who you think is honest, less partisan, and who says things you want a President to say.
The debate website Procon.org has a very good page on the 2012 Presidential Elections. The site itself does not, to me, appear to have a political affiliation, but I'm sure die-hards on either side would see it as skewing opposite... such is the nature of political blinders.