Through the years the integrity of the EVOO packers has greatly increased. Your name brands are a pretty sure bet of good quality. There are various flavor profiles in EVOO. It can be used for frying and will enhance the flavor of most foods. Stay away from "pure" olive oil. This is a blend of approx. 5-10% EVOO and refined olive oil. Refined olive oil is a clear tasteless oil. By adding a percentage of EVOO it gives the blend a little flavor and bouquet. Overall quality is low.
I have spent the last 59 years in the industry and it's a lot different today than it was years ago.
RT