I have switched from Gitlab CI to Travis CI and now to Circle CI. I left Gitlab because of a job change and was working on my Github so I wanted something that intergrated with GitHub. Thus why I tested out the following.
Previously I was using Travis CI for my CI runner. This worked great as it was free for open source project but the con was that private was paid. So if I wanted to build a private repo I would have had to pay money.
After a lot of YouTube commercials for CircleCI I decided to try it out. It works better then Travis as it allows me to run the correct Maven commands instead of a default command that does not run my test. It also is free for Private Repos with an API Key. So I then switched my Repos over to CircleCI.