Shaun_Max I experimented with Unity Ads vs AdMob this way: in 50% cases the game called Unity Ads, in 50% AdMob. After a while of testing I found that Unity earnings are about 2-3 times smaller than AdMob's.
Did not have much experience with Applovin though. Only used it in one game, on the 3rd tier of ads waterfall, it brings something only if other 2 levels (Admob and Unity) don't provide ads.
Never tried Ironsource. I saw a video about IS mediation, compared the eCPMs shown with the eCPMs which pure AdMob is already giving, and did not find the need to switch.
However, again, if the game starts getting several tens of thousands ad views daily (when people say it's worth to use mediation) I think I'll try them.