Having got to know Kingpin pretty intimately, and having had BBB since it was released, I have come to think of KP as a little better than BBB, mostly due to its "flow".
Art - BBB > KP
Theme - BBB > KP
Playfield layout/shotmap - KP > BBB
Audio - BBB > KP (just)
Toys - KP > BBB (mostly due to the gun mech shooting the ball out from under the playfield)
The ramps are a work of art in their placement and the way they add to the classic fan layout.
It has that classic nineties set up where smart rules mattered, and shortcomings not attempted to be compensated by lots of toys and gimmicks. In that respect, and with its flow, it reminds me of AFM (not gameplay wise, but as a package). The modes are great (albeit needing some work to polish unless there are better ROMs out there that I have) and a couple of clever wizard modes at the end. I am just typing an email to James with a few rules to take a look at (although they probably already have). With the rules polished a little, this will be a classic.