Considering some of the other answers on this page, I'm editing mine to make it more comprehensive.
The conventional wisdom is: "Delaware, because that's what everyone else does" and that statement does seem to hold some water.
Here's the wikipedia article on Delaware Corporate Law
A line from the article:
Delaware is well known as a corporate haven. Over 50% of U.S.
publicly-traded corporations and 60% of the Fortune 500 companies are
incorporated in that state.
and here is a writeup from the Delaware Department of State - Division of Corporations
Why do corporations choose Delaware? I think the answer is not one
thing but a number of things. It includes the Delaware General
Corporation Law which is one of the most advanced and flexible
corporation statutes in the nation. It includes the Delaware courts
and, in particular, Delaware’s highly respected corporations court,
the Court of Chancery. It includes the state legislature which takes
seriously its role in keeping the corporation statute and other
business laws current. It includes the Secretary of State’s Office
which thinks and acts more like one of the corporations it administers
than a government bureaucracy
One of the other posters brought up a point about California, for example, requiring you to register in CA regardless of where you incorporate if you are doing "repeated and successive transactions" in CA. For you this is particularly relevant with one of your co-founders who you say does most of your transactions living in CA.
So, to summarize, the answer to your question of "Is there a best practice for this sort of thing?" is:
Yes, figure out if there is a reason to not incorporate in Delaware and if you cannot find a good enough reason, then go with Delaware.