I used to have ER-6i set but then the left earpiece went silent. Now I use a set of Sennheiser CX500. The sound quality was probably tad better with ERs as CX500 seem to have bit heavy on the bass - of course this depends what kind of music one listens. CXs have also volume adjustment on the cable which is nice.

My major gripe with ERs is that quite deep in to the ear, and therefore are bit irritating for long use and also they tend "extract" ear wax so that the ear piece has to cleaned often. Additionally, when I used them in the office and peole were asking something from me, it came quite a chore to take them out and put them back in. CXs isolate quite well (used with smile on airplane) + they are easy put and take away.