The 6spd auto is a renowned gearbox. It is very smooth, to the point where up shifts through the gears are barely noticeable. I believe the same box is used in Bentley's, BMW 7 series and the like. In terms of "speed", because there's no taken to change gears 1/4 mile speeds and acceleration will be faster. I have the 6 spd manual and made this decision because I like to "feel" as though I am driving the car, rather than the car driving itself. The Auto is nice but takes the fun out of it. The manual gearbox/diff is known to be a little clunky at times, and it's a reasonably long throw between shifts. The long throw can be minimised with a short shifter. At the end of the day, all you need to do is decide what you will use the car for and go from there. Good luck and enjoy!