my experiences concern the time after the guarantee period of 2 years:
got 3 A8s with air suspensiona and at all 3 i had to change the air-kompressor and at each A8 i needed to exchange one suspension strut. very expensive repairs i can tell you.
have 2 S-classes now and i changed on each car the air-kompressor and once a suspension strut.
needed to exchange several times the relais which is responsible for controlling the right air-pressure in the struts.
needed to check the cables, which burned through 2 times.
mercedes asked me to leave the car for 1-2 days the need to check the air loss on the struts.
(and i have to pay the observation time

)
i can tell you this, air suspension is very complicated, and very expensive to repair. the garages are not very experienced with it and they normally dont repair, they exchange the suspected parts.
i m not sure how well this new system is reliable, but i m afraid not. i mean if merc really developed 30 years this ABC
and it turns unreliable like this, so how reliable is the new 10 years developped new technique.
i wanna drive my car and not wait to get it back from the garage. i had enuff experiences with the w210 and 211.
spend a lot of time in the garages, until a merc ingenieur came from stuttgart to check what my concerns are.
they offered me to exchange the car, which was uneconomic for me.
as for the driving comfort, i agree on mercedes air-suspension, the car is smooth and soft - on the audis not so, the car is even on comfort mode too hard (not my own opinion - my guests say so too).
as on the dynamic side - i can only speak for these 2 cars - nothing beats normal springs.
(i know that the merc and the audi a8 have dynamic or sport modes but these turn in my eyes the struts only harder and put the car lower) - its like: i m in control, i m in control, i im control, i m in ..... shit i m not!
with the adjustable suspension on the bmw 7s - i have not so much comfort as in the s-class, but at a fingertip i can change to sports mode where the car is really more dynamic and gives me the right feedback, not to mention the free choice to set the engine in sports mode or other modes-
it depends on you what u prefer, a car which is smooth, too smooth to give you feedback for a better controlling or
if you want to be always assure that you are in control of the car but you feel some corrugations.
in real this is like: you get out of the merc after 800 kms and you dont feel them really but you never really are aware of
the cars real situation.
or you go 800 kms with the beamer and are always in full control of the car and you still feel enuff relaxed.
i mean for the guest the first option is always the best but for the driver i think the second is better.
not to forget that the right choice of tires and air pressure on them makes a big difference on the driving feeling