depends, are you using eldar or corsairs???
personally your best bet is something to compliment their speed, so fast troops, and a fast HQ are great.
They are like a ground version of a prisim cannon, so they are going to be shooting at tanks and heavy infantry. What makes them decent is the invul they get from being so far away from the shot. Use this to your advantage, as well as the EJB movement given by jetpacks and they are a decent, if not expensive unit.