Use what you know. Jenkins is at least mostly self contained, and the development process seems to be modern and on-track (especially with security updates after the bump to JDK 11).
Try to wrap things in Makefiles or some other abstraction so your CI-side scripts are basically `make lint; make build; make test; make dist_packages` or similar, and you're not locked into any specific CI system and can easily jump ship if required.
