Mainstream: Fedora. It has been rock solid for me, while at the same time adopting the cutting edge of the Linux ecosystem (latest gcc, latest security stuff, etc.). Also a lot of exciting things happening, like Silverblue, CoreOS, OSTree, etc. For stuff that needs to be really stable, you can use RHEL or a derivative.

If you are willing to do something more alien: NixOS. But be aware that it can be a deep rabbit hole and time sink.