2GB vs 1GB really depends on usage, i leave my box on 24/7 so the extra ram is a benefit and you future proof. There is a AML bug thats causes ram to fill up on all theses boxes eventually leading to a freeze, Kszaq has addressed this in 007 but i haven't tested yet. For me 2GB was a requirement since i tried 1GB box.
S905 vs s905x looking at kszaq development it seems installing LE is easier on s905x since the kernel has the dtb files, so eventually i think s905x will become the norm.
8/16 remember about 2GB is set aside for ROM including LE eventhough LE will never use it. Usable space is 4.7GB or 10.8GB for all kodi data. My current install is already at 3.6GB which is mainly tmp data such as youtube trailers.
As of today I'm perfect happy with s905 until i buy a 4K TV i have no need for s905x.