Revising an old thread because I'm a new M3 owner:
I chose DCT even though I felt I had made a horrible enough mistake in '09 by buying a Carrera with Porsche's PDK. I traded that car for a 6mt Carrera S within 6 months and just took the enormous financial hit to have the manual transmission car I should have purchased in the first place.
However, I owned two 6MT E46 M3's and thoroughly test drove a couple of manual transmission E92 M3's before deciding on DCT for this particular car.
Porsche's manual transmissions are not to be missed. They are so smooth with perfect clutch pedal feel and linear engagement and the stick throw from on gear to another so effortless and with such a connected feel I swear you can feel the tranny fluid and all of the perfectly engineered moving parts through the shifter.
However, I'm not a fan of the shifter feel or clutch pedal take up on BMW's M3 whatsoever and it was a disappointing part of my E46 M3 ownership experience (although a heck of a lot better option than SMG or SMG II which, IMO, was horrific). While BMW seems to have improved the feel and functionality of the 6MT with the E90 cars it is still no where near as perfect feeling as Porsche's manual.
Personally, I love a properly design, great feeling manual, but I just don't feel BMW has got it right enough in the M cars to truly satisfy anyone who's owned considerably better feeling manual transmissions.
My 2010 335i, M Sport, manual tranny (short shifter with added weight) was perfect.......almost right there with the Porsche manual. You could shift gears so smoothly that passengers felt like they were riding in a car with a fantastic auto tranny, but the M cars have a different feel to their manual transmissions altogether versus the 335i M Sport's and I, for one, don't like it.
If the E9X Manual felt like the transmission in my 335i I would definitely have gone that direction with my M purchase.
Porsche = Manual Tranny
M3 = DCT