firstly the g class mercedes was designed for off road use. it was first sold in 1979, made for military use and was avaliable with all diff locks as standard.
the never models may be plusher on the inside, but they can completely hack it off road firsly look at this...
http://gwoa.co.uk/uploads/forums/2177191…
this is the 400CDI model, and this guy carried on through this water with no troubles. if you are not pursuaded look at these videos
http://www.clubmbf.com/Contenus/Sorties/…
http://www.clubmbf.com/Contenus/Sorties/…
in one of the videos a club member is driving a g55 described on top gear as 'the coolest car in the world' and he takes it in all the same places at everyone else.
i have owned jeeps, i have luckily never owned landrovers, but my g, even though i sold it late last year, was the best vehicle i have owned, its more exclusive than a maserati quattroporte, its as practical as an mpv and is superb off road.
if you are based in europe go for the 400CDI diesel, if america the 500 is your only option, but gas prices are cheaper over there and the diesel quality is poor for such an engine.
the choice is yours, but have good fun off roading anyway