They are two separate and different phones.so are the nexus and s3 the same thing? as in 'Samsung Nexus Galaxy SIII'? or am i confusing two phones?
the SG3 has Samsung's Touchwiz and is, from what I heard, arguably the best phone on Verizon right now (depending on what you're looking for). You want a phone that can be rooted and ROM'd and the Nexus has the most amount and arguably the best dev support.
That's not saying the Rezound doesn't have a great dev support, but if you want the latest and greatest software FIRST (in this case JB), then the Nexus is the way to go. The Rezound is a great device and it would indeed fit your needs as well, but again, many would agree that the Nexus is THE device for rooting and ROMing.