There are three basic issues you can use to help you choose a leader:
1. Their ideology: What their philosophy of government is, what they think the government's proper role is, and where they draw the line. There can be a very significant difference here, but it's hard stuff. Also, the two main parties in the US (and mostly elsewhere) are primarily the Politicians' Parties whose ideology is limited mainly to getting elected and reelected.
So if you're stuck with politicians, you can try:
2. Their character: If you can't get the other guy on their vision of government, maybe you can get them on personality? Whether they are stiff (Nixon) or at ease (Obama), whether they fool around, whether they are corrupt, -- and best of all -- whether they are hypocrites, the number-one favorite of all political campaigns and of the press: Palin doesn't believe in sex education in school and look - her kid gets pregnant, which shows she can't control her kids (who can?) and that her ideas don't work in the real world. That's why the Demos are jumping on this -- not because they would do any better, or because they really think sex education and condoms in schools would make a terrific dent in the teen pregnancy rate (studies are mixed), but because it makes Palin look foolish. Zing!
3. Their competence: Would they once in office be able to actually run things and get people to do what they want? This is a combination of basic competence (ability to get things done at all), plus their influence over the political process in Washington. For an example of the latter, Obama amuses us with promises to "go over the budget line by line" and eliminate waste and unworkable programs; in reality, as being a Senator he knows full well, he'd run into the Congressional buzzsaw protecting special interests. (Unless of course the entire Congress is Democratic, and then you can eliminate "waste" easiliy since that, as all know, is championed only by Republicans!).
Hillary ran into this early with questions by ultraconservatives about whether, as a woman mind you, she'd be competent to run the government and put her finger on the big red button. Well, they don't wonder about that any more, but instead are scared of her. (Belatedly, after she lost the nomination, there were articles about how poorly she ran her campaign compared to Obama, whose campaign machine ran like -- well, like a machine. I found that a far more interesting comparison.)
The variant on this is the Experience quibble, which gets very muddy indeed. Obama doesn't have much "experience" and neither does Palin -- presumably, the only person with experience for this job is a past President, wouldn't you think?
Then you get into the question of *what kind* of experience -- legislative, or executive? Is a Senator or a Governor better suited, experience-wise? Of course, when neither has been in higher office more than 4 years, nobody can claim they have experience enough with a straight face -- can they? So as a campaign, you zig and zag among these three methods of deciding on a candidate, pickiug your strength and their weakness, and forgiving your guy/gal for their weakness but being very unforgiving of the other gal/guy's weakness. Which wouldn't be so bad if the voters, who know better, used any kind of sophistication in making their decisions.
The great thing about being a Libertarian is that the second and third issues don't mean bupkus to us. We're voting for our candidate's ideology -- his vision of how the country *ought* to be run. We don't care if he's *actually* competent to be President -- he never will be! He hasn't got a prayer, so who cares? What an enormous relief!
Nor do we care about his morals or hypocrisy or character -- like I say, he's never going to win an election, so we vote for him strictly as a powerful symbol of our ideological beliefs about right government. It's quite relaxing not to have to worry about any of this, or pay much attention to the noise at the major-party level.
And it's quite depressing to know full well that no matter which pair of major-party candidates gets elected, we're just as screwed -- the details may vary slightly, but the trendlines are just bad, bad, bad, because their ideologies mean they will choose bad options, push for solutions that don't solve anythng, and never, never learn from their mistakes.
But then, we voters don't either, so why should they?