To start off this topic...there are many brands of engine control management (ECM)available in the market as there are candy bars to select from. There are many opinions on different ECM, too.
However, lets set the parameters right. Don't be bothered by the specifications variation of ECMs. A 32bit processor need not be any better than a 8bit processor when you compare the final results in the drivability and reliability of the car. Besides, an engine cannot tell the difference wether it were controlled by a carburator or electric fuel injection. All matters is the ECM must be able to tune the engine to produce optimum output....ie max power, least fuel and still be reliable.
For many years, I am the die hard of the PowerFC on my previous S14 and now in my S15. It provided what I demand well. I wanted an ECM that I can plug and play myself. I wanted to maintain the program myself after the tuner has done his job on the dyno and road tune. So far, my PFC gave me 100% return for 4 years without a single glitch!
However, I am now toying the idea of a HKS F-CON Pro because of the direct support from HKS in our shore. I shall update all if and after I change my religion.
Motec M4 did cross my mind, and I had the idea to run it in parallel with my powerFC to control the auxilarys but tuning support of Motec is limited here.
I am also a user of Megasquirt. I was facinated by the fact that all the software and technical support is Open source available in the web (free).
I have successfully installed and tuned my 1988 mercedes benz 200 running Megasquirt. The car had been in our family since new, it was my dad's car and all has been stock. I recently rebuilt the engine, installed and upgraded the autotransmission, replaced the carburator set up with full programable EFI controlling the fuel and spark. I am in the process of refubishing the paintwork and all exterior trim at the moment. the car is running well now, return better mileage and much better torque and power. I'm now in the process of fitting a TPS as the current throttle body has a lack of space to accomodate the TPS. It should run even better after the TPS is installed as I can vary the acceleration control by part TPS and part MAP.
Interestingly, the megasquirt fuel and spark maps only offer 12x12 matrix. Many will tell you it is crude and cannot control well. i will tell you otherwise as I've used it and it is every cent on par with the most expensive ECM when drivability and reliability is a concern.