Bricklink Studio is proprietary — LeoCAD is fully free & opensource.
Bricklink Studio's `.io` format is closed — LeoCAD's uses LDraw's `.ldr` format which is fully open & well documented.
Briclink Studio available only for Windows & macOS — LeoCAD available for Linux, macOS, Windows and could be compiled for any platform which support Qt (including *BSD, Haiku OS, RaspberryPi, Arduino, etc.)