TL;DR: They’re same-old-same-old. When I first started trying other Arch-based distros after Manjaro, it was really a disappointment how much the same they all are. Don’t sweat it.
Longer: I came from Ubuntuland a couple of years ago, so I had a start on moving to other distros.
I currently run two computers each on Manjaro (one Unstable, one Testing), CachyOS (one v3, one znver4), and plain vanilla Arch with the Zen kernel (both with Testing and KDE-Unstable repos).
Manjaro and CachyOS both use the Calamares installer. As for Arch, while archinstall may not be THE Arch Way, it’s included on the ISO so it is legitimately AN Arch way. You just have to push keys instead of click a mouse. Big whoop.
Once installed, the differences between all of them are mainly aesthetic, with the exception of CachyOS’s hardware-optimized repos. There are details here and there that, really, only fanbois care about.
I’ve found there to be no “stability” issues in any of the six—even Arch with Testing and KDE-Unstable. Then again, I don’t use Nvidia… I just don’t know what the fuss is all about with all that “instability” stuff. A bunch of woowoo if you ask me.
I don’t game, so I can’t speak to that. The CachyOS optimizations initially seemed faster, but on my laptops (all the same make, model and spec), the Arch Zen kernel actually benchmarks higher, so I’m thinking it might be placebo effect—again, for my usage. Your mileage may vary.
If you use pacman and yay or paru, there are zero differences. If you’re a pamac user, shelly does the same thing, just looks and clicks differently.
I found I like the aesthetic of CachyOS’s alacritty/fish terminal and made that my standard across all three OSs. But that’s just personal preference for the eye-candy.
On your Manjaro machine, I suggest you run pacman -Qnq > pkglist-repos.txt and pacman -Qmq > pkglist-aur.txt to get full listings of what you have installed so you can replicate your software load more quickly and easily here. (You can feed the lists directly to pacman and yay or paru to automate the process.)
Although I’ve not used it, @cscs (also a former Manjaro user) has written a script that backs-up all your KDE settings into a file, that you then restore to another PC to quickly replicate your desktop environment. See https://discuss.cachyos.org/t/transfuse-a-script-to-backup-and-restore-kde-plasma-configs/8029 I also use his maclean script for routine cleaning and sera to update KDE eye candy that pacman, yay, paru, pamac, and shelly don’t handle.
I don’t use any of the new-user stuff from either Manjaro or CachyOS (the stuff on the Hello screens). Just gets in my way.
Most other differences you’ll find speak to edge cases and user preferences.
So, don’t bother sticking-in a toe to test the waters. Dive right in. It’s just a different part of the same pool.