Bill Gasarch asks: "Is it always best to vote for who you actually like best in the primary elections?"
I don't know, but it's certainly an interesting question. From what I've heard, the question of tactical voting in general elections is well-studied. But in primary elections, where one often has the choice of voting in either of two elections, there's the added complexity that you don't necessarily know which election to vote in. Some people claim this happened in the recent New Hampshire primary: independents tended to prefer either Obama (in the Democratic primary) or McCain (in the Republican primary). Polls shortly before the primary showed both of those candidates leading, and that Obama had a comfortable lead, and McCain's lead was less comfortable. Thus a lot of people who preferred McCain over any other Republican candidate and Obama over any other Democratic candidate chose to vote in the Republican primary, for McCain... and so Obama lost. (There are of course other interpretations of the New Hampshire primary results; the two main ones are that Clinton won because she cried, which is silly, and that the polls were wrong because statistics work that way.)
And that doesn't even touch on the issue of "electability" -- the person you would most like to be President isn't necessarily the right one to vote for, because a candidate that in your mind is inferior may be better able to defeat the candidate of the other party. It wouldn't surprise me to learn that in certain pathological candidates, someone who would always want a Democratic president should vote in the Republican primary, and vote for the "least electable" Republican candidate.