On my M5V that is my main heart & soul forever bass, I went through the stock Bart preamp, then a Nord, then a John East J Retro, which I really liked for a couple of years.
Recently, Spencer and a couple of other guys have been really promoting the Trickfish IPA preamp. I got curious and installed the IPA several days ago and I'm really,
really liking it a lot. To my ears, it's a more neutral, more open, but still with a character to it. It's said that with all EQ controls flat, it sounds very much like a good ol' passive jazz, which I feel is accurate, at least as I remember those basses sounding (it's been a while…

).
A good friend is having the IPA installed in his new M5V and I'm really excited for him to hear it.
Definitely a preamp to consider.
(Oh, sorry, I just realized you were asking about pickups, not preamps. Sorry. I went with Nordstrand Vintage 70s wind single coils, but there seemed to be an odd "bite" to their tone that I grew to not like. So I sent those Nord pickups to Lindy Fralin and he re-wound them to Fralin specs. I'm very pleased with those pickups now.
However, you can't just order Fralin 5-string pickups that will fit the M5V. They are shorter than the standard Fender 5/string pups sizes. And Fralin is still a small operation and doesn't have a form for 5-string pups that size (whew, finger getting tired!). That's why I sent in my Nords to Fralin for him to rewind.