Honestly, I don't care what the biggest seller is. I would guess it to be the Glock, because they can sell many thousands of units to each LEA, and sell to many LEAs.
What is more germane is individual sales...where each purchase is by an individual, who (hopefully) has done his homework.
Unfortunately, many of those individuals do their research here...and end up buying Glocks.
So I think you know what the answer will be.