The big advantage that Altium had for a while was that they were an available, portable format for parts libraries. Everybody was producing and giving away their symbol libraries in Altium format so you could always take whatever design you were given, extract the parts, fix any bugs or weirdness, and get on with life. Since those libraries accompanied the design, you knew those parts symbols had been proven out on at least one real PCB somewhere.
Then Altium went and closed those library formats so that you couldn't tear the parts out anymore. I dropped Altium right then, 100% for KiCad. I had already been doing about a quarter of my designs in KiCad, but I went all in when Altium did that.
The big advantage that Altium had for a while was that they were an available, portable format for parts libraries. Everybody was producing and giving away their symbol libraries in Altium format so you could always take whatever design you were given, extract the parts, fix any bugs or weirdness, and get on with life. Since those libraries accompanied the design, you knew those parts symbols had been proven out on at least one real PCB somewhere.
Then Altium went and closed those library formats so that you couldn't tear the parts out anymore. I dropped Altium right then, 100% for KiCad. I had already been doing about a quarter of my designs in KiCad, but I went all in when Altium did that.