Have you read any of Keith's books?
Have you driven any of the different generations?
Knowing which you prefer based on initial impressions of a short drive, might help.
Basically, the newer the better for a DD.
A 1.8L is a lightly better car to drive since it has a bit more umph. Some like the power steering, some don't, for a cruiser/shared ride, the PS isn't a terrible thing to have.
The 5-speed was pretty much the same across the board, expect to change the fluids and service the shifter/oil as its easily forgotten.
They are pretty much legos, so quite a lot will transfer forward and back. This also makes identifying their year a bit more tricky.
The torsens are all pretty much borked at this point, so its not a selling point, really. Nice if they work, but plan on rebuilding/replacing it.
The superchargers aren't the greatest solution, they tend to have idle issues and hot intake temps so their power is limited. If you don't have a OBD car, or have to worry about local emissions testing, you can put in one of FM's ECU's and improve the idle, ignition and fueling a bit. Its still not as good as a turbocharger solution for drivability and power output.
Since you're shopping used, the suspension under it doesn't really matter since you'd have to change the dampers anyway, so a set of springs, bars and bushings becomes a "while you're in there" sort of thing.
The NA/NB at this point really needs a roll bar and a butterfly brace as they are getting a bit old, squeaky and wiggly. This bumps you a class though :/
I actually liked the NC we rented for a weekend trip to the coast. It was comfy, made nice noises and even the 6-speed auto blipped the throttle on downshifts when carving through the coast mountains. That said, the styling isn't the greatest, IMO and its a bit more a cruiser compared to the other generations since its a bit heavier and shares its underpinnings with the RX-8.
Choose the one you like the color and options of, then work on the minor details that you'd want to change (suspension, power, styling, etc.) There's lots of options around to tailor them to your desires, some expensive, some cheap.