Gary,
Between the PCV team, we've towed with various versions of the E-Class Mercedes and we've always found them to be hugely impressive towcars. The intial purchase price when new can be pretty scary, but as a used buy, it's got loads to commend it. According to our colleagues at WhatCar?, electrical problems can be an issue, so check everything works before you buy - especially the gearbox, which can suffer software problems which cause irregular shifting.
Hope this helps
Nigel Donnelly
Editor
Practical Caravan