I've owned/still own Alembics with:
Essence electronics
Signature electronics
Europa electronics
Anniversary electronics
I'd offer that if you like simplicity, the Essence electronics are the way to go. Personally, it is one of my favorite setups.
If you like something a bit more complicated, but less flexible in terms of being able to manipulate each pickup independently tone-wise, the Europa electronics are the way to go. I recently sold my Europa not because I didn't like it, but because I liked the Signature and Essence electronics more - it was more me.
If you like to be able to tweak each pickup independently, the Anniversary or Signature setup is the way to go (2 X filter and Q). The main difference, as Keith has noted is in the pickup selector/pan pot option. For me, the pan pot works better. If you're running something stereo, the Anniversary electronics should be your option of choice.
I will say the Anniversary electronics are very, very trebly to my ear, but that's only my personal observation.
The Signature electronics sound more woody to my ear as well.
If it is possible, I suggest you contact other Alembic owners in your area and see if you can play their basses. This way, you can figure out exactly what works for you (and at a far lower cost than buying a lot of Alembics!).
Good Luck!
Alan