||Do your research on standalones. From my discussions with a few tuners, the AEM software isn't as user friendly as others.
Haltech is a good option. There are a lot of pros to using a standalone over the stock ecu:
1. More safeties.
2. You can add additional sensors (oil temp, oil pressure) and set it up to do engine protection should something not be right.
3. Better knock control than stock ECU.
4. Boost control through the ECU - again can be used for safeties (overboost, knock, etc).
5. You can wire in ABS sensors and do some form of traction control(ish).
6. You can add wideband O2 (again, for safety, but also as feedback control of fuel delivery and ignition timing).
7. You can add an ethanol content sensor in the event you are running E85 for automatic compensation.
8. You can ditch the MAF(s) and go with MAP.
Those are just some of the things I could think of off the top of my head. I figure if you are starting with a relatively stock car and want to go all out, standalone is the best way to go. You're not much more money when you factor in buying a boost controller, second MAF, Selin Translator, etc.