It really depeonds on a quite a few factors. Do you need knock control? Do you need many additional outputs to control ntirous, IAC (idle control), etc, etc. Do you need the advanced logging capabilities of some? Closed loop operation for cruising? Or is this going on a race car that is seeing straight line and WOT only? Wideband integration?

Your choice in engine management varies depending on the answer to questions like that and many more.

Once you decide what you want, making the choice based on a feature set is trivial. There is no best engine management out there, at the core all they control is injector operation and timing. Its up to you to decide if you need/want the bells and whistles.

Another deciding factor is that you do not want to be running an esoteric engine management that is not widely used by the racing community. When you run into a problem its good to be able to ask others with similar setups to see if they have been through the same trials and tribulations. Trust me, you do NOT want to be R&Ding an EMS on your car unless you like wasting money.

I have tuned stock ECUs, AFCs, VPCs, Haltechs, AEMs, Microtechs... they are all similar once you get the concepts down. For a full street car needing to maintain AC, knock control for shitty gas, advanced logging, wideband integration, closed loop tuning for AFR, and the ease of plug and play..I would go with an AEM. Race car, straight line, good gas all the time, Haltech is nice and cheap. All my cars will run an AEM, because I build full street cars that idle, kick ass, and that actually drive on the street frequently. So it fits my needs very well.

EDIT: I will say though, that short of a MOTEC, *none* of the EMSs I have tuned have even close to the same logging capabilities of the AEM. In that regard, the AEM wins hands down.