GPS first. Communications satellites are higher, and harder to get, and GPS is more critical. Knock out GPS, and you don't just impact map reading. You turn back the clock 30-50 years on the DoD's inventory of precision standoff munitions. And EVERYTHING is a standoff PGMs these days - Tomahawk, ALCMs, ATACMS, JDAMs, WCMD, JSOW, any artillery platform larger than a mortar...anything not aimed by eye, laser, or radar has its accuracy cut by a factor of 10. Even the SLBM fleet.
Losing the communications satellites would be a disaster. Losing GPS would be catastrophic.