Since this is such a competitive area, and sales, specials, & policies can change often, we found it helpful to build a spreadsheet of various vendors, and make quick spot-checks at order time (
usually about 4X per year for us). Sometimes the same vendor has the best price—sometimes another does.
We
do prefer to sticking with a particular vendor, but things can change, and stuff can happen.
Best (IMO) to be prepared.