OK, as the pandemic quarantine is ending, a quick review of the headphones that I have. With Apple Spatial coming out and lossless as well, I've hooked up my headphones to the very best that there can be:

1. Sennheiser HD-650. These are my most expensive headphones at $400 and they sound it. They are open-backed and the review says their bass is lacking which is probably true, but the neutral mid to highs are wonderful. I'm using them with a Focusrite Scarlett, so it's backed by a nice DAC, but it is hard to tell. They are really comfortable to wear for sure. Looking at the frequency response is really nice and flat. The really great thing is how comfortable they are. 2. Sony WH-1000MX3. The MX4 is out these days, but the MX3 remains a really nice headphone at only$219 since it is from 2018. The great thing is that it is Bluetooth (so you can't get lossless audio, but candidly, I have a hard time hearing the difference this really makes even with the fancy DACs that I have). The big complaint I have with them is that out of the box, they are boomy so they are +3dB and then drop in the mid-highs at 4KHz. But if you apply an equalization filter that blows out the clear bass, they sound really good. Not quite as wonderful as the HD-650 but very nice. Plus their noise canceling works decently on the plane, so a really nice set for on the go. Plus, they have a microphone, so you can use them for Zoom calls. Definitely, the most versatile set I have and did I mention they are comfortable for a 5 hour plane flight.
3. Shure SRH-440. These are \$100 headphones that I've put together with a decent DAC. As over-the-head sealed headphones, these are actually remarkably good. The review says that they have a pretty neutral sound and I would say that's probably true. They are pretty plasticky but that sort of comes with the territory. By measurement, the bass rolls off, but the big issue is a big treble peak at 10KHz and let's face it for my ears, they run really hot and the plastic earmuffs kind of stink.
4. Airpod Pro. Well, because well they are compact. Surprisingly, RTings.com found it had decent frequency response but I would agree they are flat but do roll off quite a bit with their bass. Makes sense, they are not sealing so it has long roll off after 80 Hz. And they are noise cancelling so good for a coffee shop, but not so much an airplane.

Of course I haven't broken out my Etymotics ER-4i (lost a bunch of them) or ER-6, but I think that this is probably a good tradeoff.