My usual style is to run Arch Linux with a Tiling Window manager, such as Herbstluftwm. Because of this I am sure that it will be no surprise that I generally prefer X to Wayland. There is no version of the Cosmic desktop that runs on X. So this is also bit about my time with Wayland.
So lets start with the positives. Cosmic with the tiling feature has actually been a very good TWM, if you overlook a few bugs.
I have also enjoyed using the Cosmic suite of apps. Such as Terminal. The terminal is based on alacritty, which is a terminal I used for a long time. Although, just like normal alacritty it does not support image previews with yazi. This is why a few month ago I switched to kitty. But its not a deal breaker and I can happily use the Cosmic terminal.