You mean a good version of Avic NextGen is better. Previous versions of NextGen are a joke. Even Avic have some problem, but it launched a lot faster now. Skin is anoher story: Pongo has a long way to go. I still preferred a good version of Primo+dimkaWa skin.
Most people (especially the newbie) preferred NextGen because of the cleaner (more consistent) UI. I don't like NextGen skin architecture where everything are bits and pieces. Primo skin was simple; one .zip file per skin. If something goes wrong you know where to look and debug. Since NextGen skin are scatterred via ux, it's very hard to find problems and fixed them. And NextGen is more resource intensive than Primo (not that it matter to most). I still enjoy playing with Amigo running on android 2.3 with 320x240 res.
NNG created NextGen as a solution to their branding for various car manufacturers. Components and functions are like lego blocks where they can mix and match to suit their needs. At the same time they revamp the licensing strategy where you need license not only for proggy but also functionality (ie map/poi/building/etc...)