If you like Germany, take the 77. If you like places you've never heard of, take the 76.

In all seriousness, the 76 flies quite a bit more. I averaged around 350-400hrs yearly on the 76 when I was there. The 77 folks seemed to chase the planes around via airlines. To answer your question, I don't think there's a better QOL on one fleet over the other. Also, you aren't really given the option to pick which aircraft you're on. They will give you the next available class, whether it's 76 or 77.