The developers have some problems (I dont care). Well.. developers of recalbox make dificult to release a nightly because they say "NOOOO PEOPLE CANT TEST IT". Seriously? Even so they not suport nightlies, they just block people to try because "hurr isnt public (unless you compile yourself)" but you're able to compile yourself. Usually this makes one thing: of course the "stable" recalbox have several bugs and lacks of several things, they just don't accept people reporting, wtf? So it's all about what they want, not about what is good or what is better.
Well maintained but they don't accept changes, they don't accept something that works perfect in other OS, they don't accept something that can be improved to be better. For example, recalbox have an onscreen keyboard, they could be ported to the (not well maintained now) emulationstation, but the answer is "why not using a keyboard?", really? If you use a pi in your room will you attach a keyboard to scrap every time you need it? So.. probably it's chained to how the thing would be. If the author of emulationstation don't put any good feature on it, you'll end using a 3 or more years old software.
It's about everything that retroarch can support. Well maintained, nice interface (not as good as emulationstation, but at least is heavily developed). The community is pretty well and accept suggestions. And of course, there's nightlies are there, you can use it, test it and report any bugs.
Now you now the truth.