I would go with the GSR, parts are cheap and plentiful. WHO HONESTLY gives a shit that a bunch of people have them? There are a ton of ludes out as well. Not so many 5th gens b/c they were way overpriced by the end of their run. Price tags were close to the $30k mark. The lude has always been honda's test car. It was the 1st to have a hydraulic clutch, disk brakes, and state of the art suspension. The biggest reason people choose the GSR over a lude is from, the engine, transmission, weight, price of mods, price of body panels, PARTS INTERCHANGEABILITY, these are all things that people want. We all know the engine and tranny in the ludes are a little disappointing. The engine has things that other honda engines do not have that people wind up removing anyway like the balance shafts. The tranny doesnt have that sporty of gearing for the weight that the 4 cylinder engine has to haul, it has cable shifters that are known to break. The B series engines and transmission are near indestructible and replacement parts for them are much cheaper and easier to buy.
I remember when I had my lude, it was such a pain to work on the car. Putting the clutch in the car was a huge pain. Preludes have always had some goofy cross members and shit on the car.

Basically if all you want to do is drive the car and have a nice handling car thats not a turd buy a lude. If you want to buy a car that you are going to try to make fast, track race or drag race the gsr would be the better choice. Stock for stock the GSR is probably the faster of the 2 and the lude being the better handling. The 5th gen lude takes most of its styling from the 88-91 years so it has a little more old school styling, back when hondas had low longer hood lines.

The prelude type-s HAD the ATTS system, you are thinking of the prelude SIR-S spec that has the LSD tranny and NO ATTS.