I haven't tried the GNex but I do have a Nexus S 4G collecting dust. IMO, Samsung phones are horrible, I've yet to have a decent one and I'll never buy another again after being burned by 3 in a row.
The NS4G was what I was using before I decided to give the IP4S a try and that thing was just plain crap, the worst cell radio I've ever used and I could barely get wifi to hold and to me, those are 2 VERY important things you need to have work to be able to have your phone usable as a PHONE, LOL.
I have absolutely no loyalty to any brand, I just want a device that works well and keeps my interest, so far my jailbroken 4S has held my interest longer than any phone I've owned and I've yet to have an issue with cell or wifi reception and I've actually stayed with this thing for 6 months which is 3 months longer than I normally have a phone active for

Damn, I hate having expensive hobbies
The 5.01 JB has worked fine for me so far but I wouldn't mind having one released for 5.1 so I can "spring clean" the living crap out of this phone and start fresh with a clean install. Since I'm new to IOS I've experimented the hell out of this phone so I'm sure I have a lot of residual junk that needs to go but I'm glad I did experiment and play around because now I know exactly how I want my phone customized to my personal needs.