I've been using an off the shelf Stage II map from Cobb Tuning using the AccessECU reflash system and I honestly couldn't be happier. The performance is night and day and it's smoother than stock zero issues.

I'm sure I could of spent 2x-3x the money on a custom dyno tuned ECUTek map for a few extra ponies but I couldn't justify the cost in my case. If you have the money and don't mind spending it go for a custom tune. Stay away from EBC/MBC/AFC as I've yet to drive a WRX that run smoothly with these gizmos.