ebruoot is correct however:
CM6 is newer and has parts from a newer leaked build. Possibly more customizations built in. BB 0.4 is based off a leak from a week or two prior. Both Roms are built from source I believe and ran very very well on my Droid. I am missing a lot of details but I am too lazy to look them up again lol. Try both, most recently I had great results with CM6 RC-2. But when BB 0.4 was the hot stuff that worked great for me too. Glad I can help haha