Advice, SGIII or GNEX on Verizon?

Quick back story, I recently sold my 4s so that I could "upgrade" to a 4G phone to keep my unlimited data on Verizon. I hate my Samsung Stratosphere with a burning passion. I enjoyed my time with my Droid X1 but have always wanted to get an iPhone so I got one and love it. Now I'm stuck with this piece of garbage until October but I have some extra money burning a hole in my pocket and a curiosity with Android 4.0/4.1. So my questions are...

1. Where is a good place to get an off contract phone? Craigslist is pretty barren for me where I live, and eBay scares me, but maybe that's an irrational fear?

2. Should I go with the GNEX or SGIII?

If this phone works out well, I don't mind waiting to upgrading to the new iPhone, but if I do, I'd like to keep and play with it, emulators and what not. From what I've heard about the SGIII, it will take a significant time to get updates, and of course it has a skin on it. I'm "skilled" enough to tinker with the phone if need be and I was wondering if I could put stock ICS/JB on the SGIII through rooting or something, because in that case, it seems like the winner to me.

Thanks for reading this, and any info would be very much appreciated.