What is better to preserve - mental stability or creativity?

Some of the world's greatest minds are often mentally unstable, and their well being has suffered from it. Examples of this can include Stalin, Andy Warhol or Nikola Tesla, all of which might have benefited from psychology as we know it today. Assuming a link between creativity and mental illness in a way that forbids us from choosing "both" or "neither", what is better to preserve? Mental stability or creativity?

See also: "Do you think genius is linked with mental instability?" and "What is ethical regarding a brilliant mind that is also unstable?"