I've been running Cachy for a few months - it just works.

I picked it because it appeared to be easy to install Arch (which I've run before, btw) with sane defaults.
But that's exactly what Endeavour is from what I just read.
I don't know if the purported optimisations provide any real world benefit, but the major reason I went Cachy is it being the flavour of the month.
For the time being, it's where a lot of focus is for new development in the gaming space.

I've been running cachy for about 9 months. It's great. Just works with my older hardware and allows me to game. Updates are easy, rollbacks can save your life (I've rolled back once after I fucked up).

I run KDE with nvidia (gtx 1070 ti) and it's all just ... great.

I previously ran debian then mint.

Based on the experiences I have seen with others, it looks like CachyOS has more software installed out-of-the-box (compared to EndeavourOS being more minimal). Both look similarly easy to install and offer many different DEs (I think CachyOS has a few more though, but you could manually install others)

I personally use EndeavourOS as I like that it's more minimal and don't really care about the gaming optimisations of CachyOS. It seems pretty neat though, so I might try it out one day if I get a newer computer that would benefit from those bits.