I vote based on the performances of the night, but of course how many times is colored by a couple of different factors: personality, who I think might be in danger of getting booted, how far in the competition it is. The first couple of rounds, I will vote for anyone I think sang exceptionally - sometimes as many as 4 contestants will get my vote, and if any 1 or 2 really really stick out, I'll vote for them. At this point in the game, I don't care who it is (i.e. whether they're my "favorite" or not).
About midway through, after seeing how contestants have been doing overall, I will still vote for a couple of different performances if they really reach me, but I take into account the overall progress of the performer. Last season, Carmen could have had a week where she was absolutely amazing, and I would not have voted for her, because I felt she was the absolute weakest singer in the competition. If someone sings well and I think they might be in danger of being booted (in favor of someone who was really horrible), I will probably give them a bunch of votes to keep them in the competition.
Towards the end, I vote for my favorite, or favorites, but at that stage of the game my 'favorites' are determined by my belief in their singing ability. In AI1, I really liked Nikki a whole lot - her personality, her look - but I could not vote for her because there were others who were clearly better singers. In AI2, I thought the final 3 was right on. I would have been happy with any combination ending up in the final 2. I voted for Clay over Ruben for his personality and consistency - bu I would have voted for K. Lo over either of them in the final 2 because she was the best technical singer in the Top 12, and had made such an amazing transformation. (I also expect the Kimberly would have come in 2nd if she'd made it to the top 2).
The only time I have voted purely based on personality, not on the singing, was for this year's Group 2. I tried my darndest to get Bree into the Top 12, even though she didn't have a very good performance, because I was psyched at the possibility of seeing someone I could identify with in the competition - but Bree didn't really blow it any worse than the others in her group. Had she made it to the Top 12 and not improved, I would not be voting for her.
guinevere