The SD1 is very, very tubescreamer-esque in tone. It has that nasally, mid hump thing going on. And with humbuckers, its almost impossible to get unity gain, and it sounds like your dry signal is coming thru plastic, surrounded by a buzz of drive. That's the classic problem with Op-amp overdrives into clean amps.
The OCD is pretty far from a Tubescreamer, as far as overdrive pedals go. A lot more "amp like" to my ears. I love mine. V4 is by far the best yet. The OCD has pleasant mids, and a nice solid bass repsonse, and the switchable High peak/ low peak gets you a good variety of tones. I've gone thru a TON of overdrive pedals, but the OCD is the one I settled on.
It all depends on your application.
If you want to set the rebel relatively clean or light breakup, and use a pedal to get a pretty accurate tube-y crunch, the OCD will be great.
If you want to set the rebel for light breakup, and use a pedal to get great SRV ish tones, the BB Preamp would probably work better. Likewise, the BB preamp is a great choice to boost an already heavy-overdriven amp. The tuneable high and low EQ works wonders. The BB is basically like the best improved-tube-screamer I've ever heard.