Matt Miller (#4) (3/8/2013)
Besides - all of those sorts methods you mentioned presume a flat list structure. The internals for how tables are structured are anything but flat.In short - I suspect the actual answer is "none of the above".
I'd tend to agree with Matt on this - my suspicion is that it will use a heavily optimised hash table in most circumstances but the only people that can give you a definitive answer would be Microsoft.
You could try asking on MSDN.