The ideal ruler is one that is both competent and not corrupt.

If that is simply not available, for whatever reason, I'd prefer an incompetent but non-corrupt ruler over a competent but corrupt one any day.

Someone that is competent understands his job as a ruler and knows how to utilize his power to achieve whatever end he wants to achieve.

For a corrupt one, those ends are about personal gain and self-gratification, for a non-corrupt one, they are about the peace, well-being, and safety of his people first and foremost.

An incompetent, non-corrupt ruler tries his best for his people, screws up and fails out of honest mistakes.

A competent, corrupt ruler could actually do good for his people, but for his own selfish reasons chooses not to and might even actively sabotage his people for a bigger paycheck.