I think GSP had the best psychological game in the business, although he was also obsessive to the point that it was tiresome. GSP was highly self-aware, but had underlying confidence in his skills. He didn't need to massage his ego by talking a lot or having excess bravado.
Mir IMO was somewhat delusional and always thought he was better/smarter than he was. Ronda was completely delusional. In both cases I think it hindered them as Ronda never improved and Frank fought stupidly a lot of the time, often acting as though others couldn't hurt him. If they had been more self-aware they would have fared better. However, that said, if you aren't self-aware it is still better to be confident than not confident.