I had a DSG MkV, and love it. However, to get the fun out of the DSG, it seemed like you had to drive it fast, especially to get the fast up-shifts. With something like the DCT in the M3, where you can toggle the transmission shift from "light to heavy," you can enjoy more of the dual clutch goodness without going at very fast speeds.
But, the tradeoff was always making fast starts at stop lights, and the general comfort of an auto. And, I had (still have them) two manual cars at the same time, so I could always scratch the manual itch, one of them being the S2000. I say that because after driving that manual, driving most other manuals isn't as fun.
If I had to do it over again, as long as you have access to manual in another car on a regular basis, I'd go with the DSG. If not, then get the 6MT as you're always going to crave driving a manual.