They're different animals.
The RC is a boost pedal with very little gain available (just a touch of hair at the higher settings). It's quite transparent and great for pushing your amp a bit harder without changing its fundamental tone. It also sugar coats your treble in a very nice way.
The BB goes from clean boost (but with more colouration than the RC) up to medium gain with plenty of crunch and sustain, but still retaining lots of clarity, smoothness and note separation. It also has something of a mid-range bump, but not as much as a tubescreamer.
If forced to choose, I'd take the RC. It's subtle, sweet, and I never switch it off. It's an essential part of my clean and low-gain sound.
If you like your tones hotter, the BB is more suited, but be aware that if you like hard, gritty, high-gain tone, you should probably choose something else entirely.