Well, I think both are based on personal definitions, so it's rather subjective, of course. But, I've known very successful people who were miserable human beings. And, I've known happy people who, in the eyes of the "world" were not successful.
I think I read somewhere that there are two kinds of people who reach huge success in business:
One is the type who is passionate about business & success--the kind like Cowell, who just want to be rich (or hugely successful). CEO's of major corporations tend to fall into this category.
The other is the type who is passionate about something that they then find a way to make loads of money doing. Your company founders are often this type, as are artistic types--writers, etc.
And, the older I get, the more I believe happiness is a learned skill. I know some people who seem "born happy"; who have better dispositions from the beginning. And, I know some people who seeminlgly have everything and yet are always complaining and are in fact, just miserable.
Personally, I think I've made a conscious choice to be happy or get happy since I've been an adult. (Often easier said than done, of course.) But, I made choices to be successful most of my life without even realizing it--good grades, awards, promotions, raises, etc. So, I wonder why the difference in the two?