Before I bought CX300, I read a lot of reviews and comparisons with Shure E2C. I was lucky to find two very good deals on both of them so I bought them both. I paid CX300 for $20 including shipping and Shure e2c for $40 with free shipping. I used them for a month now and here is what I find:
They are both much better than average earbuds (ex: apple earbuds)
Bass: CX300 is much stronger than E2C (if you like bass, you'll love CX300)
Clarity: E2C produce more clear and clean sound than CX300, because the bass on CX300 is so strong, it overshadows midrange and highrange sound a little bit.
Comfort: CX300 is much more comfortable to wear than E2C, I can wear CX300 all day and not being sore. With the E2C, it is hard to choose the right earbuds and I have to wear it right (I have to push them deeper into the ear canals) to receive a clear sound and a decent bass.
Cable quality: E2C have the best cable quality, much longer and thicker than CX300. That being said, CX300 cable is not too bad, but it can be a little short for a tall person.
In conclusion: I am happy with both earbuds, I used CX300 for outdoor and at work because it is comfortable to wear, and easy to put away. But I enjoy the E2C in my home when I just want to enjoy the quality of the music.
Sennheiser CX300 is good buy at $20 to $30 price range. And E2C is good at $40 to $50 price range. If you pay more than that, you pay too much.
Last word, if you want to enjoy richer sound of a better earbuds, you should rip your CD a least 260 bit-rate or higher. Believe me, it make a different, you will hear sound you thought it wasn't there.