Between the 930 and 3901, the 3901 hands down. The hard chrome gas system, barrel, and shell lifter alone(possibly lifter only on the 390) is my deciding factor. The 930 is a slightly better value at >$500 New, but I have bought two 390s for $525 NIB, Walmart versions, but the made in Italy no shell cutoff model. I have both and the 390 is probably the best gas shotgun readily available today.
If Mossberg would toss the chrome piston and magazine tube of the JM version in the street model 930, then they would have a serious contender.
I like my 930s, but I love the 390s!