Both are good shotguns. I've had many Mossbergs/Mavericks and bought my brother one of the H&R Pardner Pumps. All have been reliable and all are good values, IMO. Both makes have foreign parts, but what doesn't these days?
By law, no guns are made in Mexico outside of military arsenals. Many parts of both Mossbergs and Mavericks are made in Mexico of steel shipped in from the U.S. These finished parts are then shipped back to Eagle Pass, Texas where they are assembled into firearms subject to Mossberg supervison and QC. The H&R pump guns are, of course, built in China. You can safely assume Marlin/H&R has a solid QC program in place as well.