https://www.cnet.com/best-vpn-services-directory/ is areour review of VPN services. Select a few of the top 10, and then check if they have an Android app and if the quality of their app (it seems that 'ease of use' is your only criterion) is as good as the quality of their service. Since ease of use is rather personal, it's difficult for anybody here to give an advice for you.

It might be that the best app and the best service you find are not free (or maybe the app is free, but the service isn't). Then it's up to you to decide between quality and price.