I moved from MainStage to GigPerformer a couple of years ago. I have never used Camelot. I thought MainStage was a mature, feature rich solution that did all I wanted it to. And the bundled plugins were excellent (I especially miss Sculpture). But, I wanted a OS-agnostic setup (I generally prefer Windows and didn’t want to be commited to MacOS), so I moved to GigPerformer.
GigPerformer has a nice interface and I generally like it better than MainStage. I have used it a lot for a couple of years now and know it better than MainStage. My use-case is quite complex, though. Much more so than what I used to do in MainStage. So I can’t compare them fairly.
GigPerformer currently have some frustrating limitations in features that means I have to do a lot of scripting and creative work-arounds. Especially for getting hardware and software to run in sync. I also have random crashes, (probably a plugin, though, idk) and it seems gear using bluetooth midi (at least the Roli stuff I have tested with) makes all midi in GigPerformer stop working. I often get audio dropouts despite large buffer and sometimes hanging midi notes. (I don’t if I use the same plugin standalone). So, while it is too late to try something else for the live performances I am preparing, I am not currently 100% confident it will behave when on stage. Despite these issues I like working in it. Having the scripting functionality is a life-saver. My biggest complaint is some missing sync features.
And yes, I know I should report feature requests and bug reports to the devs. I haven’t yet.