Versions need description

Hi, I have question about versions of SuiteCRM. I noticed that on download page we can choose two versions 7.7.x and 7.6.x. Both versions are updated with security fixes etc. What are differences between these versions?
The bigest one that I noticed is new responsive theme in 7.7.x that is not production ready yet. Why this two separate versions are mantained ? Is 7.7.x a kind of development, streamline branch and 7.6.x more stable and production ready?
From informatnions that i gathered people rather use versions older 7.6.x on production environment. Please correct me if i am wrong.

this is the main difference between those two version

best regards