I also am not new to airsoft but certainly not a veteran/expert. But i have
never heard nor can comprehend how you can have an "unrepairable motor failure." Buy a new motor, or even a new gearbox if that's the problem, but every airsoft gun is repairable...
Worst case scenario, not even sure if it possible, is that the motor combusts and blows up. The body, gearbox, stock, and most everything should still be fine, just buy a new motor and hand grip...
Anyways, back on topic, in your question you said, "between a GBB pistol or a pistol" but the UTG M324 is a sniper. The KWA M93r's tend to have problems with cycling and will shot full-auto only or semi only for example. Kwa usually is a reliable brand otherwise though. As for the sniper, its really preferance, I have one... but just to shoot at targets in the backyard or screw around with my friends, if i ever go to a field or organized game I will use my AEG and never my sniper. And if my AEG's battery dies during a game, or its gearbox locks up, or its motor combusts
, then I can use my pistol (side arm). Lightweight, compact, fun to shoot, and its easy to run but thats just my preference and two cents.