From my point of view, your free software license represents a marketing effort. But it's a highly specialized kind of marketing - it's your marketing to development communities.
From another point of view (also one of mine), your license says something about the kind of community you see yourself being a part of. And, when you make this choice, you are excluding certain kinds of participants and inviting others. But community is not just a license, it's also how you treat others, how you see them, and how they see you, and the kinds of activities they find interesting (and/or sustainable - sometimes but not often the same thing).
A license is also a cost. For some people this will be a moral or ethical cost. The more desperate the startup the bigger an issue cost starts to become. Related is whatever small bit of return the startup can get - this is the babyfood that it will need to survive and grow.
Ultimately, I think our systems of economics (and if you pretend we only have one you are fooling yourself) demand diversity. There cannot be only one good choice when talking about all startups. There can be one good choice when talking about a specific startup (but for a few, multiple licenses might be a good thing).
Not that I have ever spent any time thinking about these kinds of issues...
Finally, note that while what I am saying here is so overly general as to be entirely useless, there are other [almost conflicting] ways of thinking about these issues which can also have value for a startup.
Carry on...