Outsourced IT development Differentiator

Just musing if I'm a CTO/Start-up or a business owner, looking to outsource some/all of my technical effort. How should I go about it? What is it that helps me in deciding where to go, whom to entrust such a critical piece of my business?
On a Weblog, They suggest what to do in contract to make it legally binding, but not much on how to decide. A lot of literature is also there, to tell you, when or what to outsource, but whom to? Forrester and other such market research organization continue to publish studies that tell you that this business is close to several billions, and still increasing. Still, very few guidelines on how to select a IT vendor. Now, vendor selection as process is beaten to death, but in this case the (new development) success rate is abysmally low. I mean what data I should seek from a vendor to evaluate their maturity, is it instincts based, is it subjective and only experienced veteran can make a good decision? Now, don't get me wrong, I understand that "it depends", essentially on ,what I'm looking for. But why should I choose TCS over Infosys or vice versa. is it only cost arbitration?
Ok, let me look from the vendor eyes, If I'm CEO of a outsourced company what should I do to differentiate my company from the others. A differentiation that is solid, covers a broader spectrum and is obvious. A differentiation that let's me charge a premium on my services.
It could be a niche, which is ok, but in these days of open source, Internet a long term niche is hard to maintain, more over if this is a new niche, it'll take a lot of time in educating the market.
Let me ask this again, what could be the next disruptive thing that can change this market.
If I'm a US based company then how do I compete with outsourcing destinations in India,China and others. What I could do that is hard to emulate and gives me long term scalability?
huf ...., too many questions or is it only one?