Colin
When I decided to get my first Alembic, I really struggled with all the choices.
Probably the first thing you have to decide is what scale length (Long, Medium, or Short). My first Alembic was a medium scale Spoiler. The medium scale length was an easy transition from having played long scale basses for years. My second Alembic was a short scale SC bass. The short scale was a easy transition from the Spoiler. Then I got my long scale Series I...I felt like I needed arm extensions after having gotten used to the SC!!! Now I can go from one to the the other without much trouble, but my short scale is the most comfortable bass for me.
The Spoiler electronics are simple but flexible. Your only decisions are what PUPs (via a PUP selector switch), to Q or not to Q, and then tweak away with the tone knob. The Signature electronics (found on models with somebody's name on it) have a blend knob rather than a PUP selector switch and a Q for each PUP. The tonal pallate is expanded with this package. The Series I instruments are a different animal. The PUPs are single coil with a dummy coil for noise cancelling. The PUP selector switch is back, but each PUP had its own volume knob as well as a 2 position Q switch. Be sure to read about the Q switch: it allows tweaking that far exceeds the typical tone control. Several other electronic packages are available, but the above 3 give you an idea of the possibilities.
Lots of body shapes are available. Some work better with a given configuration. You probably would not want a long scale bass with a small body secondary to neck dive. For the same reason, you have to be careful with 5-6 string small profile bodies. I don't think I've ever seen a short scale in anything other than the small profile body.
If you are thinking about a new build, the last (and most complicated) thing you have to consider is the wood recipe. There is a lot to consider with an Alembic. It's not like buying a FJ...I'll take the blue one!!!
Be sure you play a few before buying. However, unless the instrument is used, some dealers will have a Nigel Tufnel DON'T TOUCH IT!!! policy. Call ahead of time and be sure they will allow you to play the instruments. You will notice an immediate difference between the Alembic and your other basses just holding it.