Do you like to drive 'sporty, and control the car? Do you like rowing your gears, and having that precision RPM control, the ability to shift when you want, not when the computer thinks it's saving you gas? (Yes yes, you can throw it in 'sport' and 'shift' the gears yourself in steptronic, but it's still nowhere near the same thing).
It's really all about how you drive. Do you have a latte in one hand and a phone in your ear constantly when you drive, or do you yell at drivers like that as you go by? (hehe)
If you're looking for 'performance' reasons, there are slewfuls that say 'Manual' and none that say 'Steptronic'. Comfort reasons, Slewfuls for Steptronic, and nil for Manual.
Or did you mean.. SMG versus Manual? (That's a little different)
Welcome to the forums btw! [driving2]