As soon as you want the sports diff box checked you will have cut down your market to about 10%? ACC is fairly rare and I think heated seats might be too. For the HDD jukebox it needs to have the MMI Nav plus.
My experience, last year, when I bought mine, aligns with this. ACC was a must but of the 20 or so cars available at the time, only one had it and the shortfall in the rest of the spec didn't make it worthwhile proposition. So I focused on other must haves, like Sports Diff, Super Sports seats, active dampers (so full ADS), B&O, power tail gate and Parking System Advanced (rear camera).
The only minor option I wanted and didn't get on mine was heated seats. But, I wasn't going to turn my nose up at a cracking example because of that.
I've be led to believe Mech units fail due to a lack of regular oil changes.
My understanding is that the most common reason for the Mechatronic problems is the PCB failure, where the circuit 'tracks' lift, due to a reaction with the fluid they're submersed in. Clearly changing the fluid at the recommended intervals is a good idea but having just done mine, I'd suggest the filter is the important part of the equation. My ATF fluid was clear and clean, the filter was black, so it had clearly been doing its job very well.
With that in mind, depending on the mileage on the examples the OP's looking at, make sure the filter has been changed too, if the S-Tronic has been serviced.
To answer the questions that haven't been answered - I think which options are a must, is a personal thing. Although I wanted the Sports Diff, as it seemed to be recommended, I don't drive the car in a fashion to actually need it. It's nice to be able to play with it though!
I would suggest the active dampers are recommended as comfort really is quite different to Dynamic and makes driving on our roads much more enjoyable. B&O would also be something I recommend, even though I hardly use mine. When I do, it does sound good. And I was in to car audio for a while in a previous life.
Adaptive Lights is a good one, for obvious reasons.
Have a read of the online brochure and see which options appeal and use them as guidance. I would suggest you don't take the dealers word for it on options though, as they're either incorrect or more often, not a complete list. When you find the car you like, get the registration and give Audi customer services a call and ask them what options are fitted. You'll get teh full breakdown then.
Paul
