Use either or both depending on the aircraft and what/whether I'm listening to.

On RJs, the noise is an order of magnitude (10dB) louder than mainline a/c, so I'll typically use both - E2c's plugged into my audio source (MP3 player or laptop) and QC2's over the ears, with the cord removed.

On international flights I'll usually just use the QC2s, with foam earplugs for sleep periods.

Audio on the QC2s is very good, and the ANR is adequate for most flights - on 777s they're all you need. The QC2s alone allow one to converse with others (FAs etc.) while the "double-bag" of EC2's in-ear plus the QC2s on ANR mode pretty much blocks ALL sound, inhibiting normal conversation.