OEM with a re-flash, and I have absolutely no regrets. I can keep control of things like the alternator and A/C compressor while completely changing the fuel and spark maps. In this day and age, stand-alone for the Focus is a huge waste of time and money for 99.9% of us IMO.
On that same note, does anybody know what Turbo Tom is using? I think he's still running the stock PCM at 500+ hp, but I'm not sure.