[Tigerhawk]

I wouldn't say the HD600 is master of none, they're highly praised for classical and a different flavour for rock music.
 

 
If you take that wording out of context, then yes that's not really something I'd say about them by itself. I just used that saying as a way to describe how you can get by listening to most styles of music and get a respectable sound with the HD600. I definitely vouch for how well they do with classical, especially good recordings that offer a lot of depth/detail for the room in which the sounds were recorded. With just the right recording, it can be a near magical experience with such an airy, natural sound. This is true not just for classical, but also acoustic and/or live recordings, over an expansive amount of different genres/styles. 

 

[Ze_Blitzkrieg]

  Listening Habbits
As far as what I listen to on an everyday basis it really is a little bit of everything. In an effort to give you some idea of what types of stuff I like and if I had to quantify it I'd say that generally my listening habits are:
Rock - 45% of the time - example artists: Blink 182, Linkin Park, Queen, Avenged Sevenfold, Muse, Awolnation, Black Keys
Electronic - 25% of the time - example artists: Krewella, Daft Punk, Skrillex, Nero, 
Pop - 10% of the time -  example artists: Madonna, Lady Gaga
Classical - 5% of the time - example artists: Mozart
Folk/acoustic - 5% of the time - example artists: Avett Brothers
World - 10% of the time - Rodrigo y Gabriela, Taraf de Haidouks, Kocani Orkestar, Shantel
 
Desires
Having ready many reviews on phones, I'm sure many of you know that they tend to sometimes focus on how neutral they are. That is what I used to originally start searching, but the more I think about it the more I am not sure it matters to me. I am not monitoring a recording in a studio and listen only for fun. My equalizer is generally set to flat, but that doesn't mean that I like flat listening. In fact, I find that I prefer
Bass: Tight with a slight emphasis, but not if it trades for tightness and control
Mids: Strong and transparent
Highs: Detailed and stronger than neutral, but not over emphasized
 
Needs
I don't know exactly what I want, but here's what I do know that these headphones MUST satisfy.
-Over ear design
-$300 would be perfect, $400 is doable, and $500 would only be for a truly perfect set that I couldn't live without
-Tight bass
-No muddy sounds anywhere
-Better performance than my current set of phones
 
Contender
Sennheiser HD600 ($330)
-Many people seem to regard these as better than the 650's, but they also seem to justify it with the fact that they are more neutral which isn't necessarily what I'm looking for. They also don't seem to be known for their bass.
 
Sennheiser HD650 ($405)
-I was leaning towards this set of phones given the reviewers saying they were a bit bassy and darker than the HD600's, but the fact that they have a reputation for being more muddy makes me pause when I consider the $400 price tag.
 
Fostex T50RP mk3 ($140)
-I read that these are planar, but for this price how can that be? They seem to be on the cheaper end of things and may be a good value, but are they better than my current set? Lots of people/companies seem to have modified variants based off of this set, so does that mean that they're just good for a starting point or that they NEED modding to really shine? I am not really interested in changing the next set of phones I get.
 
 
So with all of that I'm hoping someone maybe has some input given my listening tastes. Can you recommend ones that definitely do not meet my criteria of that I'd most certainly be disappointed with? Any contenders that I didn't list and should consider? I'm open to any and all feedback!
 
Thanks 

 
I'd like to start off by saying our musical taste/listening percentages are fairly similar, save for "Pop" and "World".  With that being said, a good "all rounder" is the best way to go in my opinion.  I've owned several headphones over the years that have sounded really great, but in more narrow bandwidths musically speaking.  The K701's for instance, sounded really good with strings and classical in general, but I found FAR too fatiguing for everyday listening - particularly with rock music.  The hot spots with some symbols just pierced my ears personally, though I know I am more treble sensitive than most of my friends it seems.  However I use the K601's (with K701 pads) on a daily basis for general computer use (YouTube videos, gaming, etc) and have no desire to replace them for this function.
 
IMO though, I have found Sennheiser to be the best for all around music satisfaction - meaning I can throw anything at them and it sounds very pleasing.  Both the HD600's and the HD650's provide a great experience and I really believe people vastly overplay the whole "woolly" and "slow" tag they've received.  Ultimately, music always has great body to it from these headphones, with having never personally been left thinking something sound "thin".  AKG's, Beyer's, etc. . .have all sounded "thin" in some music genre or another to me.  All of this being said, I am not saying the HD600's and 650's are the best at one thing, others out perform for the best EDM for instance, but they are great at essentially everything.
 
I also have the Mad Dog headphones, with Alpha pads, which you may know are a modified version of the T50RP's.  These are great headphones, with a very easy treble and great bass hit to them, however I would not recommend these over the Sennheisers unless you required closed headphones (I used them at work for instance).  I got the Mad Dog's when searching for a "Sennheiser-esque" closed headphone, and like what I was looking for, they perform "well" with anything I throw at them, and are easy to listen to for hours on end with absolutely no fatigue.
 
And when talking about the HiFiMan lineup - I'd probably look at the HE500's (find a used pair on here in great condition).  I've not heard the new HE400i's or whatever they are called now, but the older HE400's I found to be fatiguing and particularly "V" shaped in their sonic response.  Possibly good for EDM, but not pleasing for any other genre IMO.  With the HiFiMan planars though, you'll need to consider your amplification.  The Sennhesiers will sound really good with decent source and power, and scale some with good power, however (in general) planar's can be power hungry.
 
. . .just my 2 cents.

 

[DangerClose]

 
As far as open or closed, I have only ever had a lot of experience with closed but have listened to open and think they'd be a good option. I'll be around some other people, but it's not library quiet so as long as the open cans aren't like loudspeakers a little bit of noise is okay. That is, I should be in an area where there is a little ambient noise and where it is okay to make some noise as well, but I can't have a set that is extremely loud. I understand that is pretty subjective and hard to measure. I'd say for the sake of finding "the perfect set" I'm looking at all open back options.

 
You're right, it's subjective.  If you plan on listening at "fun" volume levels, it might be a bigger problem than you expect.  Something like a AKG 701 is very open.
 
Another problem with outside noise is if there is little or no outside noise, the easier other people can hear what you're hearing.  But if there is more outside noise that helps cover up your leaking noise, then there's more outside noise you might hear if the headphones don't isolate well.  
 
Turn up some music on the headphones you have now, aim the drivers towards you if they pivot, and that's how loud some open ones will be.  Some will be even louder since the back will be wide open and the velour pads don't block much, so they could be like 1.5x as loud. 
 
A big problem is, as you said, you're not sure what you want.  You simply haven't listened to enough headphones, so it's likely your next headphone won't be your last.  One that isn't on your list is the DT880.  You have DT990 on there, but you said you want strong mids, and that doesn't have it.  It has clean mids, but not strong mids.  It even has textured mids, but they are thin and so it can be hard to tell stock.  Some people say 770 is basically a closed 990 with a bigger v.  You'd have to read up more on that.  If you're willing to use EQ, you can flatten out the v-shape a bit if you don't like it.  The bonus is that DT990 is a "hi-fi" headphone but is often a very good value.     
 
DT880 is flatter.  More even.  The mids may actually sound more thin (yet overall correct) since it doesn't have the bass of the DT990 that helps thicken things up a bit.  Again, a DT880 + a little EQ can go a long way.  Both of those also don't leak as much as various other open-backs. 
 
If you want an AKG 712 or similar, to save some money get a K701 or Q701 or K7xx.  The first two are thin stock and will maybe probably need some EQ or physical modding to thicken them up.  Though the bass is certainly tight and no mud anywhere.  I have a hard time recommending these for music without eq/modding.  The K7xx sounds thicker.   
 
It's hard to recommend $400 headphones if you're not sure the sound is what you're looking for.  Various current $200 (or less) headphones used to be priced much higher not all that many years ago when they were considered some of the best in the world.  And if a $175 headphone turns out to be not quite the sound you're looking for, you spent less, and it's probably easier to sell, and then you're one step closer to knowing what you really want. 
 
And then there is soundstage size to consider.  If that matters.