OD-20 is the answer to all your (and everyone else's) overdrive and distortion problems! seriously!

if not, then I'd go with weslaba on this and go with overdrive. though I'd take an sd-1 over a tubescreamer for classic rock. the sd-2 doesn't sound half bad either (this is going by the models on my OD-20, which may or may not be perfect replicas.. though they sound pretty damn good)