I don't have any good information for you since I've never used Hangouts, but I'm switching from an iP5 to a Note 4 and I'm looking for some information on this as well.
Nice thing is that you can see all you Gmail contacts online and have gchat with them in hangouts. You can now make voip calls with hangouts and do video chat as well with one or more people.
I prefer the hangouts interface. Also you can choose to send a hangout (Gchat) message instead of SMS if that contact is in both. Other than that no other benefits.