My criteria would be:
1) The company has to be reasonably small. Not so small that there is a four year waiting list, but small enough that there is some exclusivity.
2) The frames have to be handmade. Not "handmade" in the Trek sense of the word, i.e. human hands might have touched the frame while it was being made, but handmade in the old world craftsmenship sense of the word.
3) The frame has to be available with custom geometry if I want it.
4) The frame has to cost enough that not every other bozo on a group ride has one.
5) Sort of contradicting 4) it cannot cost so much that I think I am getting ripped off. For example when I see the cost of some Specialized frames, which are manufactured in Asia, and see that for less money I can buy something handmade in the U.S. I start thinking I am getting ripped off big time. Another example would be the cost of a ti Serrotta compared to a Moots, which I consider to be better at ti.
Right now for carbon I would go for a Parlee. For titanium I would go for an Ericksen, which is made by the original founder of Moots. For steel, Independent Fabrication. High end aluminum does not really exist anymor, but it used to be Klein.