Ulib.ucl.addUser is more raw.
It doesn't require the TINY bit more overhead of ULX checks/balances.
It would be the most efficient way (if wanting ULib to control your group access)
It wouldn't log to your ULX logs "Console added user to group"
game.ConsoleCommand method requires ULX, so therefore, has a nano-milliseconds of overhead.
Logs to the ULX log files.
Also, you don't show it, it requires a line feed after the command "\n" (true if you're running a ULX command or not)
Those are the differences I can think of.