Okay Greg, first in...
I like flats in the following order:
1.
Thomastik-Infeld Jazz Flats; super-soft, awesome tone and clarity... they are the absolute best in my opinion, but expensive as dad-gummit. On the other hand, I have yet to wear out a set.
2.
D'Addario Chromes; I have these on both of my fretless Alembics right now. Stiffer and brighter than TI's, very articulate and a bit unforgiving. The longer I play them, the better I like them though. No complaints, I just prefer TI's for fretless.
3.
Pyramid Golds; if you like the old-school sound, look no further. I had them on my fretted Distillate for a while and really bonded with that sound, but then I tried them on my Custom fretless 5-string and did not like them
at all.
4.
LaBella 760FHBB; honorable mention for this set of short-scale flats made for the Hofner Beatle Bass. I got them by chance on a DeArmond Starfire bass, and
love them. They seem to be the perfect combination of the features I like most about both TI's and DA's. I have not tried them on an Alembic yet, but the Starfire is in the process of being fitted with some Alembic activator circuitry.
Hope that saves you some experimentation, which unfortunately is really the only way to know what works for you. The nice thing (well, one of the many nice things) about Alembics is, you can swap strings out in minutes.
Happy Hunting.