I'll concur on HFB -
I didn't get to play as much as I liked. But measured against rules-neglected Firestorm and the others, it just had the most enjoyable play experiences.
If you overlayed HALO rules on Firestorm, the variety would make that the hands down winner.
STAW is a close second, only because we have some non-cheese folks here I can play against. X-Wing would be more, but just getting some campaign style sessions going for that.