In order of acquisition (I've tried many more thanks to an audio store near me by the name of Audio46, these are just the ones I decided on keeping/purchasing.)
HyperX Cloud Pro - Purchased for gaming back when I only had an Xbox One and wanted something with good isolation and imaging for shooters. And boy, do they image well. To this day after the countless headphones I've tried, the Cloud Pro has some of, if not the best imaging out of any headphone I've tested. It took 6-7 years of owning them for the cable to finally give in and now sound mostly comes out of the left ear. So now I'm on the lookout for something better which will likely be the DCA Aeon 2 Noire.
Philips SHP9500 - These were my introduction into Open-back headphones, and while I liked the sense of spaciousness that an Open-back design gives you, I was left slightly disappointed with this one. People made a huge deal about how much better soundstage is on Open vs Closed headphones, but to me that mainly comes down to the fact you can hear your surroundings better with an Open headphone. In terms of sound, I will admit I prefer a headphone with good sub-bass extension, and these do not offer that. The sub on these practically doesn't exist unless you EQ them, and even then they lack the impact since you have to boost them by around 7dB in order for it to be listenable. Pair that with a peak at 6kHz that makes everything sound shrill and like it's playing through a plastic straw, I rarely use them nowadays and only keep them as a reminder of where I came from. They're also extremely comfortable. With EQ I would recommend them, but without it, it's a no from me.
Beyerdynamic DT 1990 Pro - Now, I read all about how sibilant and detailed these were, and looking at FR graphs of them definitely made me weary about buying them. But everything about them aside from the 8kHz peak spoke to me. Good sub-bass extension, mids that aren't offensive and slight relaxed, and the highs, ignoring that huge peak at 8kHz, are just what I like. A little bit more energy in the treble is something that I am a fan of. So I went and tested them out in person and found that for some reason, that 8kHz peak wasn't anywhere near as grating or noticeable as a 6kHz peak on the SHP9500, for example. I attribute this to it being higher up in the frequency domain, so it's slightly less audible, but still there. I did not mind it too much, and in fact for music like Drum 'n Bass and ChillSynth, I actually quite liked it! With EQ, these sound virtually perfect to me. I also upgraded them to have the Dekoni Elite Velour earpads, which makes these the most comfortable headphones I've ever worn, and with the build quality and durability reputation that Beyerdynamic has, I ended up deciding to get these and keep them for as long as possible. To this day, I haven't listened to another headphone that would make me retire these.
Moondrop Aria - These were a very simple purchase. They were cheap, they sounded great, and they're solidly built for only $79. Thanks to these I learned that my ear boosts 3-5kHz a tad too much and made these sound a bit nasally for my tastes, so I EQ them to be more in line with the USound target, rather than keeping them stock or using the Harman target. After about 9 months of ownership, the paint on these has started to chip and they feel a bit weird when grabbing the parts that have chipped compared to the regular sides. But they're definitely some of the best IEMs I've heard. Definitely deserve all of the praise that they get. Not a single complaint about their sound other than 3-5kHz is a tad too much for my ear anatomy specifically.
SeeAudio x Crinacle: Yume:Midnight - I wanted something lighter than the Aria, and I really liked the Carbon-fiber aesthetic of these. Going by FR graphs I noticed they had a slight dip around that area at 3-5kHz, so I went ahead and bought them to try out and sure enough, these do not sound harsh nor nasally to my ears. In fact, I don't even EQ them! Even though EQ is a must for practically every single headphone/IEM that I try. But these line up with my tastes about 99% of the way there. Maybe a wide-q peak filter somewhere around 100-300Hz of like 1-2dB would give them a bit more warmth, but they sound perfect to me as is so I just leave them as is. Great sub-bass extension, even moreso than the Aria, and the treble on these is just supreme. It doesn't sound rolled-off and even feels like an Over-ear headphone to my ears. Very wide and airy. So if you're a bit of a sub-bass-head like me, you will likely enjoy these.
Other notable headphones I've owned or tried: Audeze LCD-2 Fazor, LCD-2C, LCD-X, LCD-XC. AKG K371, K701, K7XX. Beyerdynamic DT 770, 880, TYGR 300R, 177X GO. DCA Aeon Closed RT, Aeon 2 Noire. Sennheiser PC37X, HD6XX, HD560S, HD800/S... There's a few others I've tried but I can't remember.
Once i have the Aeon 2 Noire I will likely be done with this hobby and move on to something more irresponsible like speakers. Though I'm perfectly happy with JBL Studio 530s at the moment. Only thing keeping me from getting them is the Yume:Midnight.
But yeah, those are my 5 headphones/IEMs that I currently own and am happy with. At the end of the day, I would probably be perfectly happy with something like a Moondrop Aria and an HD560S.