I’m sure the documentation is there somewhere, but I’ll summarise based on knowledge and experience, as this is likely better than trying to compare statistics from data sheets.
The first point is that the MX*W and Z3 devices have a standalone wireless solution that does not interoperate with other MX*W/Z3 devices or MR devices. The upshot of this is that if a site grows and you want more coverage then you won’t be able to achieve seamless roaming or the like from the MX/Z to another MX/Z or a MR.
Second point, is AFAIK the MX/Z devices are still only Wifi5 devices, there isn’t a Wifi6 option (would love to be corrected here). Whereas most of the current MR devices are Wifi6.
Third point, if it was me I’d prefer to use MR devices everywhere so that the user experience is as similar as possible, and the management and troubleshooting is as similar as possible too. You also have many more options with the MR range to get the coverage you require, 2x2:2, 4x4:4 and so on.
If it was my choice I’d do MR devices to provide all the wireless capability, then an appropriately sized (non-W) MX (e.g MX64, MX67, MX68, MX75). The only time I’d consider a ‘W’ version of the MX is cost, or if it’s a small office/home office with no more than a few people, and absolutely no chance that it’s going to grow/expand.