from my experience the Spain, Italy and bottom France ones are the best sbmm wise.
Whenever I queue without geofilter I get plat and diamond lobbies but with spain and italy I get the biggest drop in mmr but it takes a very long time to find a match, so I added the bottom france server and that way I get less skilled lobbies than normal but with good queue times.
After the demonware change it doesn't seem to work anymore especially when i queue with other people.
It just sucks that it is now in the Netherlands because from my experience whenever a server from any game is located in the netherlands you get a lot more cheaters and worse hitreg, that's why i force the UK server for R6 Siege instead of the Netherlands one.
This Season I was playing Siege on the Netherlands server and my kd was dropping to 1 (normally i'm a 2kd in siege) so I switched to the UK server where I see the same skill level (platinums) but now suddenly all my bullets register and I bounced back to a 2 kd, it is now even 3 for the season.
So in short, whenever a server is in the Netherlands I can't play because of shitreg.
Also I have 9-16 ping in The Netherlands and around 20-28 in the UK yet my hitreg is way better in the uk. And on top of that I play shooters around 10 hours a day and aim train a LOT so I know when a shot should be a hit, even when I record gameplay in the Netherlands server you can clearly see the bullet firing onto someones head and nothing happens yet in the UK everything is fine.
As for Warzone I can't say anything about the hitreg in the netherlands because there I only play 140hz instead of 240 but the TTD (time to death) feels way quicker in the Netherlands than when I play on italy or spain. Bottom france one seems 50/50 sometimes good sometimes bad. When the TTD feels quicker you get shot by a bullet and the next bullet feels like 4 in one (super bullet) which makes you unable to move behind cover or react at all, This problem for me is the worst in the Netherlands.
UK, Top France, Germany, Switserland seem to have more cheaters so I try to avoid them. Spain had the least amount of cheaters but it is very hard to get in to that server without a vpn geo filter combo which I can't do, Italy has some but you have a higher chance of a normal lobby over their and bottom france is a 50/50 experience but because that has the best queue times I include it in my geo filter.
Sorry for the big wall of text I really hate sbmm and whatever is going on in the Netherlands because every game that hosts over here is unplayable for me.