By sheer numbers alone, the government asks the most of Microsoft.
Of the nine companies supposedly working with the government on PRISM, six and a half —Yahoo, Facebook, Microsoft (which may or may not include Skype), Apple, and Google/YouTube(sort of) — have disclosed the number of government requests they get including the secret FISA court ones, giving us an idea of which tech company the government turns to most often. Only AOL and PalTalk have stayed mum. Of course, the numbers, only give us part of the story. The government deal required that the techies report a lump figure of all government requests — both FISA and otherwise. Because of that stipulation, Google has refused to participate — so we only know the non-FISA numbers from its annual transparency report. It's not ideal, but we are starting to get an idea of how much data the government asks of these organizations.
Most Total Requests
Below you can see a chart of the total requests over the six month period ending December 31, 2012 — besides for Google, which gives an annual report and does not include FISA orders.
By shear numbers alone, the government asks the most of Microsoft, which makes sense considering an earlier report delineating the cozy relationship between the two, in which Microsoft lets the feds exploit its bugs against foreign governments. With FISA requests the Google number would shoot up, though it's unclear how much.