They are simply the ones that fit well and survive many rounds of washing or daily use. Recently I have been testing several online eyewear shops to compare frames and lenses. Sometimes I even measure an existing frame with a ruler before ordering anything new.
If anyone is interested in real user experiences, I sometimes write short notes about the shops I test.
You can find one of the pages here:
check this link
A good store usually answers questions quickly and does not hide behind canned messages. I also check if the store explains how to measure PD and frame size clearly. Otherwise they become clutter in the closet after the trend is over. Sometimes I still make mistakes with size, so a friendly exchange policy is very helpful.
Hope this helps someone.