If it were me, I would definitely get the SCAR 17 first without question. Especially with the election coming up. They arent exactly easy to come by right now as it is (from what Ive been able to tell anyway) and its probably just going to get harder as people get more and more panicky. I just bought one last month and Im beside myself with joy that I actually own one... I doubted I ever would. After that, I would definitely go with the SPR A1.
Now, Im not saying the PS90 and FiveSeven arent *real* guns or anything, and that they dont have their uses or benefits, I just *personally* look at them both as more of a "novelty". Especially compared to the SCAR 17 and SPR A1. Theyre the kind of guns I would get for shits and giggles more than for any practical usage. That said, I would definitely go with the FiveSeven before the PS90. Ive actually been interested in owning a FiveSeven for a while now, its just super low on my list of priorities. Especially for what they go for and the fact that they use a more uncommon caliber.
So... my vote would be:
SCAR 17
SPR A1
FiveSeven
PS90