heavyweight if you are good at breaking blocks. i'm thinking about big heart for some of my guys.
edit: also jump the snap, pass rusher, sure/power tackler, etc. I haven't invested much in jump the snap or pass rusher, but both can have a noticeable benefit from just 5 points invested. some of the VAs like sure tackler require a full 15 to make a difference. it's nice to find a few that can make a difference with just 5-10 invested.