If I had gotten the AUTO.. I would have regretted it and wished that I had gotten the manual but here is the BRUTAL Truth..
I did get the manual and there are times I wished I'd gotten the Auto. Here's a few key things on the pros and con's . I guess each has some.
M6 Pros:
Nothing comes close to sounding SOO Good as the m6 rolling through the gears
A more connected interaction with the car
Blipping the throttle between gears on occasion.
Rev Match feature
M6 Cons
I have stalled out a few times at a redlight. (So embarrassing).
I have gotten caught in some heavy stop and go traffic
The clutch Chatter at low speeds (Parking space hunting). Getting much better at letting off the gas before the clutch to minimize this sound.
Notchy gears on the cold mornings
Missing a shift
Auto shifts faster :(
I don't own the A8 so can't speak on the Pro's and Con's but I'd imagine someone that does could name a few but they're probably the opposite of the M6 Con's.
One thing I will say about the A8 and I equate it to the auto's I've had before. Much lower level of interaction with the car. Just plop down in the seat, Put it in gear and push the gas/brake. That's it. Perhaps the paddles can be fun though. This can appeal as a benefit to a lot of people and others say there's much less feeling of being one with the car that you get from the manual.
Yeah it's all personal preference.