Hi
I have been personnally using ngui quite a lot, and moving to DFGUI to check it out and I will stick to it for that project for sure.
I think Ngui does things somehow a bit better, but only just, it's really I guess a question of learning above all, both have incredible features, none really are easy to work with... you will likely have a love/hate relationship with both, just because we all want to jump and do it all without having to learn and experiement first... so indeed, there is a lot of that: first learn!!! they are both incredible UI systems.
Now, DFGui port of PlayMaker is incredible, hundreds of custom actions!! so you will get more with dfgui on the playmaker side then with Ngui. Having said that, I can do everything I want with ngui as is already, by using the available actions on the wiki or on the asset store, plus Get/set property... which really is giving you access to 99% of what you need.
I still think that SpriteManager and EZGUI are fare more powerful than the new UI sdks that came later, some of the stuff in there are in my opinion incredibly more easier and actually make sense... but again, it's "expensive" to check out just for the sake of it, and I am not sure how well it's supported now.
Bye,
Jean