Definitely determination. Not only is low determination undesirable, but after a while I'll have a very determined squad and players like that won't fit in.
The exception would be young players that can be tutored up to an acceptable level.
I like groups of stats. For example dribbling flair and technique. But whenever I buy a player I look for Decisions, Composure, Anticipation and Concentration. The first touch stat is always quite nice to think about though.