If I were trying to be competitive for relatively cheap, I'd go with a garrett powermax g25-660 or the APR EFR7163 kit modified to work with an EWG. But your turbo selection would depend on the torque curve you need for your local tracks.
More practically, may depend on your classing and what your preferred tuner is willing to support. A custom fabbed garrett kit that you can swap compressors on might be ideal, but finding a tuner that will support an external boost controller might be challenging.