How to differentiate between ironSource and Applovin and Unity?

You may want to define some clear vendor evaluation criteria, otherwise it's tough to say which is "best". Depending on where your users are concentrated geographically, what type of app/game you are looking to monetize, what types of ad formats would make sense for your game/app, # MAUs, # apps you need to monetize with ads, # ad networks SDKs you want/need to include, whether you want to sell traffic direct to advertisers etc. - there may be a different answer.