Airmatic really isn't so bad. My S430 and S500 both have them. Had to replace a couple of struts due to their age, but they're not expensive, and the replacement's actually pretty easy. I was surprised at how easy it was.
ABC, on the other hand, I would avoid. Not because it doesn't feel good to drive--it does, and when it works, it's great--but rather because of two reasons that I recently learned the hard way:
1.) there is no backup in place in case one of your accumulators suddenly goes kablooey and you lose all fluid, and
2.) the expense of fixing it when, not if, something does go wrong.
The ABC car on which I learned this lesson is my 2003 S600. The rear-axle accumulator did go kablooey. Car went straight down to the ground like Homie's Lowrider. NOT GOOD. The car is currently in the shop for a Strutmasters coil/shock replacement kit; I'm reporting on that progress in another thread. Oh, and the cracked upper oil pan is also getting replaced (a $1,700 repair including labour). I am *really* not pleased with ABC at this point.
Here's how Airmatic fails, by contrast.
You see either one side of the car or the entire thing gradually getting lower. The air compressor comes on and brings the car back up to normal level when you start it up, but it gradually takes longer. This is exactly what happened with a 2003 S430 that I'm preparing for a friend. The front right Airmatic strut was clearly on its way out; you could see it at the top. It was gradually taking longer for the compressor to get the front-right quadrant of the car back up to proper level, and yes, that strut was leaking. The front one was still working fine, but the telltale sign of a very small circular crack in the upper rubber/epoxy/whatever informed me that it would eventually start leaking next, maybe another year or so. No problem, I just called the folks at Arnott, and two new front struts are on the way. Should be here this week, just in time for the 3-day weekend.
Note that the car is still perfectly driveable. I'm just getting--and heeding--the warning signs.
Compressor failures, I've found, also give you some warning. That is, it's not a sudden "kablooey" and you're scrapin' the ground. It just gradually starts taking longer to get the car to the correct level. When you hear that compressor on a lot, that's a sign that it's time to start taking a look. Compressors can and do burn out when they're overworked over time; the S500 had to have its compressor replaced for this reason. That's actually not a hard DIY job, either, with just a little attention to detail.
So, I wouldn't shy away from Airmatic. Fortunately, most W220 S-Klassen have this system.
