Got a 6MT because it felt more natural in that car.
Plus my 7 series turbo is automagic, my jag convertible was auto too (now sold thank god), no reason in having every car be a lazy car
I did however, originally have a DCT on order. Sometimes I regret not getting it because of the traffic, and more importantly the better gearing and 7th gear for mileage.
If I had to pick again now, it would be a serious toss up. I'd probably be 51% DCT and 49% 6MT. That's a tough choice.
Since I bought my M3 in March of 2008, it was one of the first ones over here with a build date of 12/07. DCT wasn't available at that point for another couple months. I was also worried about the first year reliability of a new transmission introduced to the market. In hindsight, I'm glad I made the decision I did considering the DCT lag issues, failing trannies, software issues, etc.. Now most of that seems to be ironed out. The DCT is buttery smooth and comming from the serious kick SMG III gave in my E60 M5, it left some to be desired.
I don't think you can go wrong either way. When I purchased the 6MT I had an inclination that it would be my last standard transmission BMW.