Why Google's "hangout(s)" will prevail
plain and simple -- because it's stock.
When people update/buy their android device, they'll be greeted by it first. They have the advantage of being pre-installed, guaranteeing a massive user base.
No need to search through the Play Store to find a messaging app, reading reviews, weighing which of ur friends use which app and which of them are the most important.
More importantly, my biggest gripe with a third-party messaging app has been the fact that it's a duplication of effort. as much as android guys and gals complain about storage space, we all know how precious it is... so having a built-in messenger that saves space by eliminating the need of a third party app is a big advantage.
not going to get into the whole set up, eliminating multiple notifications, managing different apps, remember which conversation was in which app... come on man.. "AINT NOBODY GOT TIME FOR THAT."