Well it depends, do you want to be defensive and tank in flashpoints? or Do you want to dish out damage or heal? If you want to tank you should go Powertech. If you want to Deal Damage you can either go Powertech (one blaster) or Mercenary (two blasters) and pick the Arsenal or Pyrotech tree. If you want to heal then you can pick the Mercenary class and pick the Bodyguard tree.