eg I've read several times that all the US presidential elections for the last 50 years have been won by the more personable or charismatic candidate, rather than the one who had the best policies.

Honestly, as someone who is politically active/aware, it's not even worth it to vote on someone who proposes the best policies, for the following reasons:

A) Politicians will promise anything that sounds good to their base. (Duh.) They may not follow through (especially if it's a big/interesting policy), either because they never personally believed in it, it was never politically expedient (or became so), or the opposition (or even their own party) blocks progress in Congress.

B) Most politicians don't actually propose real policies anymore. Not really. I'm not sure if they ever did (I haven't read deeply into the history of such things). Sure, Obama promised to fix healthcare, but no one knew anything close to what the real result would be until it was finally proposed/passed. He made a number of concrete proposals (such as closing Guantanamo which obviously never happened because of point A), but these proposals didn't amount to some kind cohesive vision in any area of policy. Bush never told anyone about his foreign policy vision of "going it alone" and making preemptive war (the Bush doctrine). He actually said in his campaign that "If we don't stop extending our troops all around the world in nation-building missions, then we're going to have a serious problem coming down the road. And I'm going to prevent that."

C) The president is (has been?) largely a figurehead without a whole lot in the way of ideas of his own. He is definitely the big enchilada and can have a profound impact, but these days he has hosts and hosts of advisors, whom he usually defers to, telling him what to do. He's usually not competent to make very important decisions purely on his own. And he'll choose his advisors based on a patronage system, prior service, political identity, etc. What you're really voting for is the party and its political philosophy. This is somewhat untrue of Obama as he has named several Republicans to top posts during his administration, with mixed results.

So, what do I consider? Ironically, it kind of comes full circle back to "shallow" stuff like personality in a lot of ways. Honestly, these days I'll just be voting for the Democrat, because Republicans right now are too insane to be trusted with anything. Maybe once the black Muslim terrorist who doesn't love America is out of office (the "food stamp president" as Newt Gingrich calls him), they'll calm the fuck down. But were there any competition for my vote from the other side (someone like 2000-era McCain or even Ron Paul), I'd try to learn about their past behavior/temperament, especially before they became politicians. It bothered me a lot that Obama showed signs of being a piss-poor politician who couldn't get anything done due to a lack of charisma and people skills in Illinois (the time to stop him was in the primaries though). It bothered me that he was inexperienced. It bothered me that McCain had well-known, severe anger issues. It bothered me that he selected a complete imbecile for a running mate, when he quite conceivably could've died during his presidency. It bothered me that George Bush ran for president with exactly zero record of having ever done anything; he dodged the draft, started some oil businesses that went belly up and had to be bailed out by his dad's friends, bought a baseball team with Daddy's money, and then became Governor of Texas against a popular incumbent purely because his dad was a conservative former governor/congressman from Texas, despite never running for any other office in his life. He pandered to his base and was president part way into his second term as governor.

I don't really care about insubstantial things like whether a candidate did drugs, had an extramarital affair, or anything like that. I'd sooner take someone like LBJ who had many repulsive qualities but was otherwise an effective politician whose heart was largely in the right place, than someone who merely looks good on paper and is handsome/genial. Right now, among Democrats, people like Gavin Newsom and Cory Booker kind of make me sick.