i own the m50... its extremely overhyped on the internet. its a decent headphone - for the $100 price range. nice warm sound to it and fairly bassy however it does have a small soundstage. good if you need something that doesnt need an amp, is somewhat bassy, you dont have large ears and you can accept the poor soundstage (i dont mind personally). i do personally like them and they have weathered many years without breaking (other than worn pads they look new) but i'm just being honest here that many will make them out to be some sort of killer headphone deal and they dont live up to that sort of hype. good, but not earthshattering. the beyerdynamic dt770 pro is a much better choice overall if you have the budget for them and an amp.
the m50 and v-moda crossfade are fairly equivalent. build quality is more metal on the v-moda's (still plastic earcups!) but the m50's are built like tanks (albiet all plastic) as well and are fairly sturdy in their own right. the crossfade and m80 might have more soundstage but the m50 is crisper and has brighter highs.
the lp and lp2 are different. they have significantly more bass response than either the m50 or crossfades - if you want something really upfront about bass and in your face they are certainly the cans for that. these are not for someone who wants just a bit more bass than the average headphone but wants significantly more.