Performance: Two powerful engines. Picking between the two depends on the depends on the depths of your wallet. The G550 has enough performance to satisfy majority of buyers. The G63 AMG moves the G-class swiftly but is expensive and burns through fuel like no tomorrow.
On the road: Way too much wind and road noise. Plus it's not all that great to drive thanks to the heavy steering which makes city driving a chore, and an old school 4x4 set up which feels cumbersome to deal with as a day to day vehicle. Off-road abilities are flawless.
Buying & Owning: Both versions aren't cheap to buy and you'll need deep pockets to run both of them. Resale value should be strong thanks to the it's reputation for military use and also off-road capabilities.
Overall: It's one of those vehicles that will sell because of the badge and it's reputation. Other than that it doesn't really offer a compelling reason to buy one. Plus it's just too expensive to buy and run one. The Range Rover is a much better package and is much cheaper to buy. Picking the G-class is clearly a status symbol because there really isn't a reason to buy one when there are so many cheaper indirect alternatives.
Likes: Legendary off-road prowl. Built to last.
Dislikes: Priced very expensively with running cost that could make you cry. AMG will burn through fuel like it's going out of style.