Well, I used to have the e3's, and found them very, very, boring. The detail is good, but the fact that so much of the bottom end, and a bit of the top end is missing is a little too much to accept given their astronomical canadian price (at retail, that is). Also, I couldn't handle them being in my ear for more than 30 minutes, since I had major ear irritation from them. But, I recently got the e2's, for $100 cdn (yielding a $150 difference), still expensive, but not so bad.
I like them a lot! Since they have that bulbous design, they don't go very far into the ear, and the unit itself is supported by the outer ear, so the constant yanking on the already vacuum sealed ear canal that I got with the e3c is not a problem with the e2c, and I've been able to use them with no problems for 2 or so hours (haven't tried longer). The e2c's do not isolate as well as the e3c's though. The highs are still largely not there, but the bass is! Midrange is superb, quite amazing, actually. The e2c's render certain songs so well you never notice there is anything missing.
For sure, though, the cx300's come very, very close to matching the e2c's. With no noise about, and songs that cover the full spectrum, you could say they're even better, but add outside noise (taking a walk..) and you lose the extra definition they provide over lesser earbuds.
Conflicting views, I know, but I hope this helps.