Yeah, EC and Seattle are great quality, as well as Copenhagen. The best recorded performances are Bristol and Glasgow. Copenhagen is the overall best bootleg, because it's got a good performance and great quality, as long as you have the right version. ;)
Earls Court's performance is definitely lacking at times. Don't listen to anyone when they say EC is one of Queen's greatest performances. People tend to confuse quality and performance quite a lot these days. :) link
Have a look at my choices of the top Queen performances, and you might be surprised by many of them!