Don't get the HD 380 Pro if you're going to be using them on an air plane, the isolation isn't that good. It leaks quite a lot of sound for a closed can. From what i've read the M50 has much better isolation. Comfort is very good though.
Sound wise i actually was quite disappointed by the HD 380. I find the bass to be a bit bloated and it feels like there is a veil over your music. Some people like it though because it has a relaxed, laid back sound.
I recommend checking out the Shure SRH750DJ. It offers better isolation than the HD 380 and has a clearer and more accurate sound.
I've never heard the M50, but from what i've read the SRH750DJ sounds a bit better. I'm enjoying mine a lot for sure.