I've been using the 2600, Matrix, CS80 and Modular, SEM
IMHO
Out of all of them, for subtractive...Modular in my opinion, is the most versatile, and has the most variation in basic audio characteristics, followed by 2600, then SEM.
The CS80 is a beast unto its own, quite different, and at first a bit difficult to predict what's going to happen, but has some great features. However at the moment there's something wrong with it and you cannot turn off the high pass filter. V2 is fine,it all works ok, but V3 is quite hobbled in that regard. Intense low pass filter sweeps will also move the hi pass cutoff even if you don't want that. Envelopes are not as snappy or intense as other Arturia apps. {EDIT UPDATE} The filter switches have been added Thanks Be to Arturia!.
Matrix looked so promising to me, and it's great with heaps of different modulation but for me it does not sound as snappy or responsive as Modular. It sounds kind of 'softer', 'mushier' compared to Modular. The envelopes don't sound as snappy or as fast as Modular, or 2600. It has some issues when both osc's are perfectly in tune - there's some inconsistent phase thing going on that makes each voice sound different. However, Matrix has the layering of patches, as does CS80. Modular, or 2600 doesn't do that so conveniently.
2600 is interesting, more raw, more organic sounding, though you can't pick and choose as many modulation sources and destinations as you can with Modular. You might find that more interesting to fiddle with. There are some sections ( the right hand side with reverb/outputs) that I still don't understand. I kind of like that it's still a challenge!
SEM is a lot simpler, not as many mod sources, but it's more a classic subtractive analog type synth, and way easy to get workhorse type sounds quickly.
Out of all, if I were to be limited to only two, Modular hands down and then maybe SEM OR 2600. I still mess with Modular and find things I haven't heard before. yes, it has some bugs, Arturia software has heaps of things wrong with it and their development / qa process is so slack, but I still love their synths to bits.
PS I have not tried JP8 at all, nor Prophet, so I'm not fully across all of them.