I live in NY and I know here it seems that Chase, Citibank pull EX. I also have USAA and the pulled ex for my amex and eq for my world card. A lot of times it seems that CC companies pull based on geography.
Bank of America/FIA, PNC, American Express, and First National Bank of Omaha are 100% exclusive with Experian in my experience.
Bank of America/FIA will use Transunion for limit increases, and PNC will use whatever bureau you ask them to. Barclays and General Electric are all Transunion people.
Lately people with mid to high 600's have been getting approved for American Express. PNC, I am not sure, because there is not much information about them. Bank of America/FIA, Barclays, and General Electric seem to be pretty liberal with approvals and low scores. I have no personal experience with scores that low, so perhaps someone who does will chime in.
For me, Barclay and GE pulled exclusively on TU and Exp. I got the below website from these forums and I found it to be very helpful...
Wonder if it helps if you're in store trying to buy something on the spot?
There are a few posts here where members got a higher limit while in the apple store making a big purchase, but im sure YMMV.
My experience (live in PA):
Cap1: all three
US Bank: TU
YMMV....but I think Amex pulling EX is pretty iron clad....as well as the infamous tri pull from Cap1.