Maybe 20%. I've never quantified or thought about it in precise terms, though. Thinking of the groups I have right now and the last tabletop group I ran at home, out of 18 players, one player had a longsword. The rest of them tend or tended to battleaxes, greataxes, rapiers, short swords, quarterstaffs, and daggers. Light crossbows and longbows have also been carried, either as backup or primary weapon.
Wow. I can't believe that out of 18 players, no one had or currently has a greatsword.