Which US prez was the most patriotic? Why do you think so?

I'd go with Abraham Lincoln.

I think he, more than any other President, realized that America is a set of ideals to which we as citizens aspire, and when we fail as a nation to live up to those ideals, the natural consequences of our collective failure are deserved (see his Second Inaugural Address).

Most Presidents have, to a greater or lesser degree, paid lip service to the set of ideals and governed using realpolitik principles.