I've owned every gas model of W126... 300SEL, 420SEL, 560SEL. I think the 420SEL is probably the best one of the bunch. It doesn't have the hydraulic rear suspension of the 560 (which believe me, will be expensive and annoying!), yet it has the same gearing as the 560, which is a problem on the 300. The 300SEL is a nice car, but it revs too high on the hwy, slow pickup, yet it gets around the same mileage as the 420.

The 420SEL is the happy medium. It gets about the same mileage as the 300 (decent), and most of the power of the 560, but without getting 8MPG city, and the expensive hydraulic repairs. The best of the bunch are the 89+ models, with their upgraded stereo systems (SO much better than pre-89 cars) and the nicer seats/interior. The pleated leather seats of the older models don't hold up nearly as well as the newer ones, and aren't as comfortable.

I agree that the W126 is the best choice for you! Once you buy one, you will love it, guaranteed! My first W126 completely changed the way I thought about Mercedes (in a good way). In my opinion they have got to be one of the 10 best chassis of all time!

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles