I recently acquired a ZTE Open to screw around with. Simply because it's an $80 phone and I'm interested in seeing new stuff (Firefox OS).

There is no question that the 8GB Nexus 4 is worth the added expense. The Nexus 4 is a premium device in every way, whereas the ZTE Open is meant for bottom-feeders. I appreciate what Mozilla is doing. But, if you have access to a Nexus 4 for $200, get that without a second thought.