Disclaimer: I own only the 535s, and have not heard the others, but as part of buyer's remorse I started to consider whether the other 3 would be better. Based on my intensive research, here is a summary of what I learned for others to add to or learn from. Call it after-the-fact justification for my purchase of the 535s over the others, or call it a summary of the available literature, or call it what you will, here it is. Correct/add/debate/agree where you want so I can fully understand the differences.
Natrual-sounding, with great mids/vocals. Mid-centric, but great depth and extension on bass, and great extension on treble. Some say rolled off, but I disagree. Bass is there when it needs to be, at times impactful, but it rests nicely in the background. Treble is sparkly and bright. Very detailed, but musical so not analytical. Separation of instruments could be better.
Very similar to the 535s in all respects, except for the bass. Bass is not as deep nor as detailed. Mids tend to be analaytical and not as lush as on the 535s at times.
Separation is great, very detailed, very articulate. But tends to be analytical and not musical or fun a lot of the time. Some say this one is veiled and that the mids sound too forward/artificial. But generally the mids are great, as good as the 535s. The veil comes from enhanced lower mids and upper bass. Many call this a dark phone, but the bass is very articulate, present, and not at all lacking. Haven't been able to find much on the treble in this phone, though.
Very similar to UM3x, but slightly more veiled and bassy. Mids not as good as UM3xs or 535s.