HD 380 Pros will prolly be the best for you. Things to consider are they are very comfy at first but the clamping force is quite strong. It wore on me. They are very flat and I didn't prefer them for music because their sig was simply boring in that regard. But I could see them being a great studio monitor. I was constantly eq'ing them to enjoy music.
The M50 is a completely diffferent sound and personally i would NOT use them for serious mixing/recording. They are a V shape'd sig and to me artificial sounding. It did not take me long to sell mine in favor of several phones I have. They are more "fun" to listen to than the 380.
Both phones are have a very long cable (9+ feet). So portability is not the best.
If I were you I would buy the 380s for recording and another pair for listening on the go. Great portables that I own or have heard: vmoda M80, Senn HD25-1 ii, JVC HAS500, phiaton ms400.
The 380s can be had for just over 100 dollars from VMInnovations with FACEBOOK coupon code (refurbs).
Thanks for the advice. I am more worried about sound than the portability factor, and don't have a lot of issue with the curled cable of the Senn 380s (I've seen people use straight cables of their own with it, so I bet I could do that if I really grew to hate the curling.) Most of all though, I really want the phones I get to have a nice listening experience. Is the flat response on the 380 really that boring for normal music use? Are there any cans out there where I can have my cake and eat it too by being enjoyable for music but usable as monitors? If not, and if you think that a flat response really isn't great for listening to music, what would you recommend for "fun" headphones, preferrably ones with enough bass and a wide enough soundstage for a good gaming experience as well? Also, about the portables you mentioned, I tend to dislike on-ear headphones, do you have any thoughts on over ear portables? (again, portability is a low priority, if worst comes to worst, I'll use a pair of earbuds to drown out those around me. Sucks, but its better than no music at all imo :P )
Thanks for the advice and any to come :)