M1/M3 Super 90s are ~2 pounds lighter but one round less (when taken to full capacity / unless you get an M1S90 Practical - 10 round mag). Recoil operated. M3's conversion from pump to/from auto is a twist ring.
SPAS12's (gas operated) forend, in my experience, had a bit more friction when pumping than the M3's. This will get you tired faster when you use the pump action. Pump/auto conversion is a recessed button. The later versions (and retrofitted early versions) have a cross-bolt safety.
SPAS12's looks are impressive but, although reliable enough, not as reliable as the Benellis. If you want a looker, get the SPAS. If you want something a little more practical and reliable, get a Benelli.
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- Ron V.