This is very similar to asking what mic is "best" for recording an electric guitar amp. The problem with a question like this is that there are many "best" choices -- it just depends upon what sound you are going for. When I was doing lots of session gigs, I would play bass on, let's say, five different songs, and we would end up recording the bass part
five different ways for those five songs. I've recorded using mics on the cabinet, taking a direct signal out of the preamp, and going straight to the board with a DI and getting the tone that we wanted from outboard gear. As for microphones that I've personally had success with, I'd agree that the MD421 almost always gives good results, as does the MD441, the EV20, and the Beyer M88. (DJL is way hipper than most folks. I haven't met all that many people who realize what a GREAT MIC this is for bass amps.) All of the mics that are used for bass drum tend to also work well on bass amps. This includes mics such as the ATM25, as well as the ubiquitous D112. I don't think I've ever personally used a condenser on a bass cab, but it should work fine, as long as the mic has enough low freq. response and can handle the SPLs.
However, if you go to most commercial studios today, you'll find that people don't usually mess with miking up bass cabinets. Instead, the bass is taken direct in a variety of ways. If I got called in for a session gig today and wasn't told what, specifically, to bring, I'd probably show up with an Ampeg SVT,
my SansAmp PSA-1,
the Boss GT-6B, a direct box, and a couple of compressors (including my trusty Rane DC24 which still sounds great on bass, to my ears) and two or three basses. This would have me covered for almost any conceivable sound that the producer might be looking for.
Brad