Same, I always vote on the person who has done the least damage, because that a sure fire way to know they're really contributing. Of course, sometimes it means I'm voting for people who are afk, disconnected, joined the game half way through, simply don't know how to play, or a combination of all 4, but it's worth it to know that sometimes I'll be hitting someone who is doing no damage because they're really, really dedicated to objectives.
Except objectives like killing the person carrying the huttball, killing the people attacking your own carrier, killing people trying to capture or defend a turret and killing people trying to plant or defuse a bomb. But all other objectives than that, they're all over it.