I have, and love both. The question is, what do you want? Here are the traits of each to help you decide:
Tone coloring/ shaping preamp: B7K
Overdrive capability: B7K
Blended Parallel effects loop: Basswitch
Series effects loop: Basswitch
Easiest actvive/passive interface: Basswitch
Clean DI: Tie
The B7K has more tone shaping options. The EQ on the Basswitch is great, but doesn't color your tone as much as it supports it. The B7K also has the best sounding OD I have ever tried. The Basswitch does not overdrive, but has a lot of clean boost on tap. The Basswitch is a fantastic hub for all of your effects to interface. The B7K does not have this functionality.
In the end, it comes down to what you really need the box to do. I use the B7K for its tone shaping, and the Basswitch for everything else.
ZWKoch, S.A.S.S. #124; Five String Bass Club #558, Wisconsin Bassist #137; Club Microtubes #7;3 Leaf #90; fEARful #91; Worship Bass #1240.