I think going for standalone should be one of the final upgrade decision once the engine has been fully done up (cams,piston,etc). For starters, I think piggyback should be well suited (judging by the price and performance). For eg, Emanage can increase about 10hp on wheel while standalone can do 15-20hp (depending on setup), I think price wise piggyback is more acceptable. But still, some will argue that Emanage is useless (no offence).
Besides, tuning a standalone for daily drive is not easy as most tuners do race tuning only. Running with a/c and all other equipments on standalone takes more tuning time and if not properly done, your daily ride will cause you a lot of headache. Car manufacturers spent years developing the ECU which involves many variables, different conditions, loads, temperatures, humidity, fuel and etc.
I think its best if you go ask the tuners directly, check to see if their standalone can guarantee your expected HP gain. A good tuner should be able to tell you the pros, cons and expected gain as per your engine's spec.