I owned both at various times, I much preferred the E2c.
E2c - Recessed highs, but have good bass and a relaxed, non-fatiguing sound. You look like shrek wearing them. Excellent choice for exercising.
ER6 - Detailed highs but lean on bass. I found the sound very fatiguing and the tri-flange tips uncomfortable.
A lot of it comes down to what type of music you listen to and your personal preference. If you like rock and rap than definitely get the E2c. If you like more laid back music and a detailed presentation the ER6 is a better choice.