I use the Tubesreamer for my marshall as a boost. So in a word, Tubescreamer. For the folowing reasons:
It works well as a booster and offers a greater amount of grit than the bluesdriver.
However, let me add that I just purchased a Jekyl & Hyde that actually sounds good as an overdrive and also sounds good as a distortion. Granted it is both and lives up to its name. AND!!! you can cascade them. It is the only pedal (so far) that works with my DRRI. I did not want to mod the DRRI and void my warranty. Hope that helped. Sorry for the plug on the JH, I just love it. Peace.