BKB is made from a 10-star rare, and an item you can buy for PDs. It is the strongest Double Saber in the game. The MKB is not too incredibly rare, but some people *coughIancough* have had a terrible time getting one.
Double Cannon is made from a 11-Star Rare, and 2 Syncestas, both of which can be pipeable from the right IDs (Both have a 1/22 drop rate from the appropriate rare enemy). It is weaker than BKB, but has 2 more ATA (big whoop, heh).
Personally, I'd go with Double Cannon, simply becuase it looks so cool. Most people won't believe that your BKB is legit, and will thusly be a loud asshole about it...
...of course, no one is going to believe your Double Cannon is legit either. XD
Teh spinny. n_n
EDIT: I are stupid!
<font size=-1>[ This Message was edited by: Eihwaz on 2004-07-21 20:05 ]</font>