GitHub is still a good choice, but working with their more recent APIs, like GitHub Actions, I feel Microsoft's touch. They're slowly changing for the worst.
The initial capabilities look similar and circle really needs a competitor with how flaky their service has recently been.
For someone who's not a pro in using CIs, it's been much easier to use than CircleCI. I never have to spend more than 20 or 30 minutes fiddling with Actions to make it actually work.
This for me is the biggest contribution to open source: normal people like me (who don't want to get too familiar with proprietary or overengineered CI tech) will be able to have CIs for pretty much ALL their projects.