And what if you find the biggest and most important branch, and go all in, and then it turns out that everyone else also had the same idea? You'll probably still be useful, but maybe you could be even more useful with another specialty.
It's why I think the cliché "follow your bliss" is a pretty good heuristic. Another way of putting it: follow the gradient of your own intrinsic motivation, and try to have fun along the way.
And make good friends!
My own prognosis is that open source development is going to play a huge role in the future, and that participating in the open source commons is the way to "network" in the software world. If an employer won't let me work openly, I'll consider that a major downside for many reasons. So I would bet on open source involvement as an important career investment.
(That's part of why I think cryptocurrencies are really exciting, but that's a longer and more tenuous argument...)