It's tough.

I like IEMs but these days I mostly use my Porta Pros when outside, they are small, light and cheap and I actually like that I can hear my surroundings. They also have way better sound than they have any right to for the price, especially with the right pads/EQ. Stock they are quite muddy but bringing down the lower midrange really makes them shine. So I have kinda stopped putting too much into IEMs since I know I just grab my Porta Pros most of the time anyway.

The best headphones sound wise I've owned so far are the Edition XS. I don't mind the slightly spicy treble and they just do everything so well, very good tuning, absolutely great detail, excellent imaging and soundstage. They can easily compete with a lot of stuff over $1000. I sold them because they get kinda uncomfortable after wearing them for a few hours and I always worried that they would break, but if all you care is the absolutely best sound for the price you should buy nothing else, seriously.

My favourite headphones I own at the moment are the HD 600. They are just so easy going. They are light, comfortable, fit well, are easy enough to drive that they work for my phone, are incredibly well tuned and easy to listen to. Sure the Edition XS have better soundstage and detail, but the HD 600 is just so easy to throw on and be happy. They simply don't have any issues in my opinion and the more intimate sound is a nice chance of pace, too.

That said, I'm itching to get the MM-100. Of course we don't know if they will live up to expectations, but I kinda miss planars, and a reasonably priced and not too heavy Audeze headphone sounds great.

And the DT 1990, I'm selling a pair right now. Honestly I don't think these are really worth it. They are better tuned than the DT 990 and they are comfortable and nicely build and all, but the tuning is still kinda wonky, if you compare them to the HD 600 you really start to wonder what the hell Beyer is doing. Sure they have detail and soundstage but the detail is not nearly on Edition XS level and overall if detail, imaging and soundstage is important to you I would buy the ATH R70X over these any day. I really don't get how these are so expensive, buying a pair of DT 990 and throwing EQ on there gets you a headphone that sounds just as good and is way cheaper, only "real" downside is a bit more plastic in the construction and no detachable cable and that's not worth spending like $500 instead of $150 or so.