What a coincidence—I just started reading the book “The Happiness Advantage” by Shawn Achor. While I’m only on the second chapter, the gist seems to be: Happiness is not a product of success, but rather a precursor. Happy people are more likely to succeed.
If this premise is true, then I think positive psychology would have an edge over stoicism, when looking forward. Stoicism might be a better technique when thinking about events in the past.
Neutral evaluation of things you cannot change, but a focus on the future states that you prefer. I wish I could have some actual evidence to back this up, but this way of thinking has worked for me so far.