[BO] Which game has more player counts currently ?

Hi guys, i catch a BO 4 on PS store on sale and the price seems reasonable for me now. But also at the same time, a friend of mine wants to resell his MW2 (2022) disc. I checked the campaign on Youtube, there are many negative feedback about MW2 (along with MW3). So now i really wonder and need some helps from you.

Of course i want to play multiplayer mode and what game is fun, grinding attracting, addicted. Recently im still playing MW 2019 on PC, but now i shifted to PS5 as playing on TV is somehow better.

For BO, the last one i played is BO Original, 2010. Since then i only notice WW2, Vanguard, and MW. Once there was a good sale for Cold war but i hesitated, and now the price went up :(