It differs by airline. I've been out of the Boeing for a time but I believe we have all pumps on for start at Alaska. This is controversial to some because leaving the A pumps on pressurizes the nose wheel steering during push. Our ground crews must install a by-pass pin to open a by-pass valve so the NWS is not active during push.
You may like this site.
http://www.b737.org.uk/ It is full of technical data/diagrams/tests for your reading pleasure.