For me there is no 'most important' quality. Said significant other will need to posses a number of qualities that will make us compatible and able to stand each other. I look for someone who is sweet and romantic. I also look for someone who is loyal, honest, and understanding. Said person does not need to be perfect, but I do require myself to be attracted to the. If I am repulsed at the thought of holding their hand, then it is obviously not going to work.
Loyalty, trustworthiness, honesty, and a lot more.
For me, I need someone who can be my best friend. If we can't even be friends, then it's just not going to work.
Loyalty....I need a gal who will always be there for me, even when we don't see eye to eye. Just being there makes one feel loved and needed
For me, I need an understanding person. That means a lot of different things but I'll sum it up as someone who can handle my moods and the occasional cold attitude without any problems.
But they also have to be reasonably intelligent or it's not going to happen.