While angular has tons of beginner hype because of the bootstrap effect (don't learn a technology, just put it in your html tags!), I've found that marionette tends to attract a more mature developer crowd, and as a framework is much better suited to building large and complex apps anyway because of the strict modularity and separation of concerns. I say this from experience both seeing and working on very large and complex apps with marionette. And if you don't believe me, ask some of the developers at Etsy, who build with marionette.
The community is a hell of a lot smaller than something like angular, but I see that as a huge benefit, especially when that means no proliferation of beginner problems, and easy access to the core team for help or feedback.
There are also three excellent books[0] about Marionette, and about 3x more Marionette questions on Stack Overflow than React questions (for what that's worth).
We introduced it into our Backbone app and haven't looked back. It's great.
[0]https://leanpub.com/building-backbone-plugins https://leanpub.com/marionette-gentle-introduction https://leanpub.com/marionette-serious-progression