I had been using Smoktech dual coils in my DCT and pyrex tanks, but wasn't totally satisfied because more than a few would get a burnt taste, even with a good juice flow to the coils. After doing some reading here on the forums, I decided to try the single coil Smoktechs from here:
Single Coil XL Tank Cartomizer for the SmokTank XL
I switched out all of the cartos from my tanks and replaced them with the single coils. I had ordered both single and double pre-drilled holes, choosing which one depending upon the thickness of the juice. Very happy with the switch. Flavor and vapor are very good, and after over a month of using these I've not had a return of the burnt taste of the dual coil cartos.