I have just voted for Primo.
The only thing in my wishlist for both apps is to be recognized as navigation/geo app by android system, or in the other word, can be an option to run when click on address in txt, webpage, or contacts.
Currently, can not find any version of app satisfies this requirement.
Then I take one step back, can access the address in contacts from app.
Primo can access address in contacts from app, while no version of nextgen can.
So I voted for Primo.
I have installed both app on my Nexus 6 and let them share maps/poi/... .
I like the map display by NextGen better.