I switched from '11 DCT to '13 6MT.
First off, I love the DCT. It's snappy, confident, works hard even on track. I wanted to get 6MT because I like manual shifting. Sometimes with DCT I would try to shift it unthinkingly as if it were manual, especially if I had been driving my racecar. I'm not concerned about 1/4 mile racing. This isn't a drag racer, it's a road racer.
Also I plan to keep this car a while and I was a bit concerned that the DCT is pretty much not dealer-serviceable -- except for a few peripheral aspects, my understanding is that they swap the whole thing and send the old one to BMW to be rebuilt there. That could make for one heckuva repair bill. I also don't like the nanny features like throwing you into neutral if you crack open your door, e.g., to see better when backing into a tight space.
Maybe I made a mistake and it will turn out that the DCTs live forever and the 6MTs need all the TLC.
But I have no regrets.