To ensure you're selecting an avocado that is perfectly green and creamy on the inside, peel back the stem and see if it's green underneath. If it is, the avocado is perfect. If you can't peel it, it's not ripe yet, and if it's brown- it's overripe.
This recipe uses Cojita cheese. This is a salty, crumbly, Mexican cow milk cheese. Feta cheese will do as well.