I have sailed twice in Cabin 664, the farthest forward Cat H on the port side. We found the cabin wonderful. Not as much traffic as the midship Cat G. There is a vibration at the rear of the ship. It did not bother my wife or I. It was more noticeable in heavy seas and most noticeable with a following sea.

If you don't think the vibration will bother you, In my very humble opinion, it would be better to save the $4K or so on the Cat G and go for the Cat H instead. Especially if you going to be able to book the day it opens and get the farthest forward Cat H.

I should add that my mother was in 669. She found the vibration to be more bothersome. She has booked a midship Cat G, 651, for our next Voyager cruise.