If it is really going to be a "life" partner, then I'd have to choose a good nature. You want someone that is going to be compatible with you and that you enjoy spending time with. Otherwise the rest of it isn't going to matter.
I've found that someone that you may not initially find you may not initially find "beautiful" often becomes that way once you get to know them. The nicer somebody is the better they look. I don't know if anybody else has noticed that, but I have.