Axient is the flagship. Broadcast, A-level tour kind of product. Overkill for most applications.
ULX-D is the workhorse. Dante, high-density mode for complex RF environments, can get a quad RX in a 1U footprint. Sits at basically the same price
point as UR. If you need a lot of channels, the antenna cascade also saves you a little rack space. If you do use these with Dante, some consoles allow you to
monitor and control the wireless systems natively from your
console.
QLX-D is one step below ULX-D. More cost-effective, no Dante but you can at least WWB it. No antenna cascade.
Below QLX-D, I try to avoid these products they serve their purpose when only a couple channels are needed and budgets are tight.
I spec'd a lot of ULX-D until QLX-D came out 5 or so years ago. Then it became hard to justify the ULX-D price tag unless Dante or the quad footprint were a necessity so most of what I do is QLX-D. The price difference between the two might become narrower for you if having Dante/AES67 would save you the cost of extra digital
stage boxes.