Firstly I own a Nexus 4, a Nexus 7 & a Nexus 10. (and an iPhone, iPad 2 & iPad 3)
I use my Nexus 7 and Nexus 10 differently so it really depends what you want it for.
Overall I would say: If you are keeping your iPad 4 then I would say get the Nexus 7. If you are selling your iPad 4 then...