I usually break abilities down into Offense, Defense, Mobility, and Utility, then pick based on what category most needs shoring up and meshes well with what's already picked.
For Offense, I recommend Bite of the Wolf because it only costs 1 pp, doesn't require a hand free so you can keep your bow up, and can even be used in conjunction with your bow during a full attack as a secondary natural attack. (Don't forget you can 5' step anytime during a full attack.)
For Defense, Force Screen is good for almost identical reasons - 1 pp, and gives you a shield bonus without using a shield.
There are some fun Mobility and Utility powers on the PsyWar list though... I don't envy you the tough decisions you face!