I am a firm believer that I would buy based on price, and
what I find when I check out a Car, (and it's owner).
Lower Mileage and Service History may well mean nothing, it is almost a certainty that a caring and meticulous owner will do a better job maintaining his Car than a Garage / Dealership, so Full Service History is a lottery.
Whatever Car I buy I know I am going to spend at least £2000 getting it up to scratch. A nice Body and to some extent Interior is much more important than a few worn Ball Joints etc, which can be easily fixed over a weekend.
At the end of the day it depends if you are an avid DIY'er with a good tool kit, or if you take it to a Garage every time it needs a lamp bulb........................
If the latter, I might suggest that a W220 may not be the best purchase choice.
Finally whatever you choose, factor in from £400 for an SDS Diagnostic system, and teach yourself how to use it .......................
Regarding SDS do not get sucked in by the nay sayers, if they do not own and have never used it how can they have a valid opinion ??
They are simply guessing
it is like their £40 OBD Diagnostic junk, it is waaaaaaay more !! Guessing like they do when the change this that and the other parts in failed attempts to rectify a problem
Have a read of our Buyers Guide in the Blue Stickies at the top of the Forum Page
At the end of the day, your money, your choice