I’m also in the camp where I won’t typically use a closed-back headphone if the situation allows me to listen via an open-back model. There are some exceptions, where I am exploiting the nature of a specific model with a particular genre of music or album, but they’re not very common.
Thoughts on a few:
Audio Technica ATH-50Mx
Cheap, comfortable, reasonably easy to drive, decent isolation, significant bass-tilt. Usable as-is for tracking, but requires EQ for mixing (Sonarworks). Can be fun for some musical genres, but not a general purpose “listening” headphone for me.
Sony WM-1000XM3
By far my favorite wireless headphone so far. ANC that beats the Bose QC35ii, 30 hour real-world battery life, support for all the important BT codecs (SBC, AAC, aptX, aptX HD & LDAC), decently listenable passively, when powered they’re even better … with a slightly warm delivery and a decent top-end smoothness.
Fostex TH-X00/TR-X00
Somewhere between a shallow U-shape and a V-shaped signature, depending on what wood the cups are finished with. I had both Purpleheart and Ebony, and definitely prefer the Ebony for listening. Easy to drive. Lovely finish and very comfortable. So-so isolation. Wouldn’t be my first choice for an all-rounder - especially in classical realms, but a lot of fun with contemporary rock, pop and EDM.
TR-X00 model is the same tuning as the TH-X00 model, but has a removable cables (see note, below*). This is useful as the stock cable is rather long, though flexible and nicely made (and its very easy to convert it to balanced or to shorten it etc.):
MrSpeakers AEON Flow Closed
The exception that makes the rule … this is a better sounding, more neutral, and more open sounding headphone than its open-back cousin … for the same price. Likes power - otherwise they’ll sound congested and lifeless/dull (not something to use straight out of a phone). Tonality can be tweaked with included filters. Not a detail-monster (though better with the black filter), but otherwise a very engaging and convincing listen. Looks fantastic, excellent comfort, supplied cables are a sane length, non-microphonic and extremely flexible. Offers the best isolation I’ve so far found in a passive headphone.
Focal Elegia
The closest thing I know of to a reference tuning for a closed-back headphone. This throws people expecting the elevated bass typical of most closed-back cans (if you’re looking for emphasized bass, look elsewhere). Fantastic resolution, excellent dynamics (macro and micro), more-open-sounding than most closed-backs. Isolates well enough for my use-cases, but vented enclosure means they’re well behind the AEON Flow Closed in this regard. Supplied in a very nice package with an excellent case, though the cables leave something to be desired - especially for portable use.
ZMF Eikon (Padauk)
A close run thing for me with the HD820 in terms of which is the most enjoyable to listen to, with the Eikon being unfailingly enjoyable, with better neutrality than the HD820 and a more liquid sense to their delivery. Solid, taut, bass foundation, that doesn’t overwhelm. Lucid, detailed mid-range, and a natural sounding top-end. Gorgeous finish, excellent build, very comfortable but quite heavy (doesn’t bother me, due to years of using Audeze cans), with average isolation.
Fostex TH900 Mk2 (Emerald)
Pronounced V-shaped signature with fast, hard-hitting bass, excellent sub-bass growl and rumble but has recessed-if-detailed mids. Top-end is both aggressive and too pronounced and benefits significantly from a pad-swap (TH610). Excellent resolution, clearly outperforming the TH-X00 line there, and in dynamics, but tonally just way off. A lot of fun with the right music and mood, but not much of an all-rounder. The limited-edition lacquered Emerald Green finish is stunning (the standard Bordeaux are extremely pretty too), comfort is high, they’re fairly easy to drive, but they’re a specialist piece and even then the price is very high given their quirks. Removable cable (see note below*), and package includes a headphone stand. Isolation is so-so.
Sony MDR-Z1R
Very warm sound, bass plays deep but lacks impact/speed, and exhibits some bloat, compared to much less expensive options. Tonality is wonky in most setups, but for some reason comes together and sounds significantly more neutral when paired with the Sony NW-WM1Z or TA-ZH1ES. Music projects with an exaggerated sense of scale compared to most cans, but the mids, while rich, get lost too easily. Top-end can be zingy. Lovely build, and excellent “forget you’re wearing them” comfort. Included cables, with locking connectors, are excellent - and include a dedicated 4.4mm TRRRS connection for Sony’s (and now Sennheisers) DAPs and DAC/amps. Price is somewhat comical for their level of general technical performance/tonality, however.
Sennheiser HD820
A striking looking (the glass panels are extremely cool), technical tour-de-force, with a not-quite-neutral tuning and absolute dependence on getting a proper seal. Their large, non-circular, pads make this unexpectedly hit-or-miss (they can seem to be sealed, and not be, very easily). And without a proper seal they’re all kinds of wonky (not just tonally). But once properly seated, they exhibit the best overall technicalities in my list, with superlative resolution, fantastic dynamics, solid, if slightly elevated, bass-punch, and the best imaging I’ve heard in a closed-back headphone.
If you’re expecting them to sound just like an HD800 or HD800(S), but with isolation, then you’re probably not going to be happy. They are the closest thing to that you’ll likely find, but that doesn’t mean that’s what they actually are in any real sense. If you don’t need closed-back/isolation then the HD800S or a modified HD800 is a much better, less expensive, bet.
These trade off with the ZMF Eikon for the bulk of my closed-back listening, with the Eikon being tonally purer and more seductive, and the HD820 being more resolving and expansive.
*The Fostex TR-X00 and TH900 Mk2 cables LOOK like they’re terminated with the same connections as the Sennheiser HD6XX line. The actual insertion depth on the Fostex is deeper, which means some HD6XX connectors will not engage solidly enough to stay inserted. Also, the Fostex models are wired with opposite polarity to the Sennheiser connections, so will play in opposite phase if using an HD6XX cable.