I bought the Audio Technica ATH-ANC23 QuietPoint Active Noise-Cancelling In-Ear Headphones. It works and is reasonably comfortable for 10+ hour flights but "reduces" , not eliminates noise. (The AAA battery last the entire flight.). One factor in effectiveness is how tight the in-ear piece fits. My unit has leakage but I have not experimented with the various sized pieces that came with the device.
One down side is the active reduction only works at cancelling relative wave forms like engine harmonics. It does not cancel out endless chattering of passengers who feel the need to talk the entire flight. If anything, it cancels out the white noise that drowns out the chattering.
The decision factor for me was the light weight low volume of the unit. Over ear units may work better than my cheaper device, but I would be carrying them around the rest of the trip.