Having recently compared (as in test-drive loaner units for a month) scopes at the $10K mark at work, mostly lower-bandwidth versions of what you’re considering: the decision should first and foremost be driven by your needs.
For example, LeCroy has unbeatable analysis tools, and I quite like their UI. But their waveform update rate is far lower than the others, so they suck for identifying glitches in real-time. In contrast, Keysight and R&S excel at this. Tek is a bit weird: they are not bad at real-time glitch capture — but only in a particular acquisition mode that disables most other features. In a sense the Tek models don’t have any obvious strength (other than offering super-low-capacitance passive probes), but they grew on me, in that I just liked using them. I will add that the physical build quality of the Tek models was the very best in the bunch.
I came across a quote somewhere (in a presentation, I think) from a LeCroy manager who said exactly what I concluded: there are two groups of scopes: “analytical” scopes focused on event capture and analysis, and “display” scopes focused on real-time use with high waveform rates. LeCroy is the leader in analytic scopes, Keysight arguably the leader in display scopes, with R&S trying damned hard to dethrone them.
(This isn’t surprising, given that LeCroy began not as a scope company, but as a maker of digitizers for nuclear research, where one captures a ton of data of an event and then analyzes it later.)
In the end, I ended up going for the MXO4, because I already had a high-end LeCroy I can use for analytic purposes, so I chose to go for a “display” scope, and the MXO4 excels at this, with both full-time 12-bit (which is used for the digital trigger, so the trigger sensitivity is superb) and above all an unparalleled waveform update rate and a great spectrum analyzer. It was a really tough call between the MXO4 and the Keysight 4000G, whose user interface is by a wide margin the most responsive of all the scopes I’ve ever used (other than other Keysights that are equally snappy). The Keysight is only 8-bit, has very small acquisition memory, the web interface and display streaming are mediocre, the user interface looks a bit dated, and the display resolution is low by today’s standards, but it’s an absolute joy to use. The Keysight is a mature product and it shows. The MXO4 is really nice in many ways, but it feels a bit unfinished in places. (Including promised or hinted features that still have yet to materialize, like zone triggering and XY mode.) I also hope R&S can hire some experienced software developers from the video editing and game engine development worlds who can help them improve UI responsiveness (which is OK, but not great), because I’m convinced it just needs some optimization.