So there's something like a midwit peak for making money. If you don't need to make much, you can work on whatever you're most interested in; if you want to become moderately rich, you can't usually afford to; but if you want to become super rich, and you're young and good at technology, working on what you're most interested in becomes a good idea again.
There's one case, though, where it's easy to say whether you should work on what interests you the most: if you want to do great work. This is not a sufficient condition for doing great work, but it is a necessary one.
When to do what you love as a two step assessment: you have a passion and a passion to do great work.
I treat passion as if it implies wanting to do great work, but that's an error. Everyone wants their work to be seen as great work. Few care enough about doing great work to do what it entails.