[Rajmun340]

Factory M3 owner, manual trans. From my experience 30 years driving manual cars (heel and toe anytime, on any road, in traffic or on a track but i don't track the M3). I think the weak link is the dual mass flywheel in the M3, not the transmission. Mine has gone bad, and actually showed early sign of being problematic right from the factory (bought new euro-delivery in 2013). i can tell from rough shifts and oscillatory like torque response after a shift that one of the flywheel circularly mounted springs or its stopper has failed. This has happened under original bmw factory warranty, but bmw failed me and refused to investigate it under warranty. A young unexperienced regional (states side) bmw engineer drove my car, without my presence (i never had a chance to meet him) escaped the issue by emailing me :the clutch is a wear item:. The nerve. All independent mechanics, three in total, told me after driving my car that's not a clutch issue.
So you want to get 6MT or DCT either way is fine. 6MT works just fine. But beware the dual mass flywheel in the E9x. I don't know if only some of them defectively built and others not. It is the weak link. Some DCT issues probably come from failing DM flywheels. Once the spring(s) that smooth out engine torque after a shift is broken, the poor dct gets more beating from the engine which cannot be good for it.