I would rate them in this order OPS OBP SLG AVG but it depends on the position. SLG is probably more important out of your power positions, OBP for everyone. none of those are nearly as good by themselves as looking at OBP and SLG in tandem would be. it's not really any harder either. if you look up a guy's OPS or OBP, his SLG is going to be right there next to it anyway.