I'm a big fan of the DCT but I think it's 2 biggest downsides are:
- it's not easy to launch, therefore not the best for drag racing
- diff is welded so aftermarket LSD's are 4k +
Everywhere else, the DCT is unbelievable. If these things aren't a concern than the DCT is perfect.
I personally prefer the 8spd because imho, it felt 90% as quick as the DCT which is amazing. I assume the 8spd is bolted as opposed to welded so LSD is only a 2k investment and it shouldn't be any harder to launch than the 6spd steptronics. Plus you've got an extra 2 gears over the N54 step and N55 DCT so fuel economy gets even better on the highway.
Both transmissions are amazing though.