If you dont want to mod the pedal or pay to have it modded, then the Tube Screamer is a great deal. It is probably one of the best stock pedals around.
As with most pedals, the TS is even better when modded. But the Blues Driver BD-2 is superb after a good mod kit is installed. It would be hard to choose.
But you did say "blues" and that word, imo, does not conjure up notions of Tube Screaming distortion and heavy grinding buzz guitar. You may be better off with a simple clean boost. Or mod a GE-7 eq pedal and use that for a clean boost. A good clean boost or eq boost into a good tube amp makes for some very very memorable blues guitar! The MXR 10 band eq modded is a real monster, too.