I own an M2, and have examined both double and single stroke M3's that have belonged to others. In terms of build quality I'd rate them all as extremely high, but I'd rate the DS M3 as the most impressive, with the SS M3 and M2 as close runner-ups. I don't think the SS M3 justifies a higher price at all. The M2 is probably the most practical one-camera-solution shooter between the lot, although an M4-P is even better in that regard.