99.9% of the players are fair. So it's a more or less a pointless exercise to single out just one when virtually everyone else behaves in the same manner. The problem is though that in tennis absolutely everything from a grunt to a disputed linecall, a 'come on', a fistpump, even the way you celebrate a victory - in short, everything that shows that tennis players are human beings instead of robots is immediately called 'unsportsmanlike.' I guess this is really the Mats Wilander behave-alike award.
I'll grant you that tennis is a pretty fair sport compared to most others, but I think you're simplifying things a tad here. True, not every fistpump, disputed line call or grunt is a sign of bad sportsmanship, but some are, and plenty of players engage in other forms of unsporting behaviour as well, on a fairly regular basis: strategic medical time-outs and bathroom breaks, snarling at ballkids, bitchy comments about officials and/or other players during pressers, etc.
There are also players - but very few - who show sportsmanship above and beyond the call of duty: spontaneously conceding disputed points to their opponent, thanking ball-kids for bringing a towel or a drink, being unfailingly gracious in pressers despite being continually baited by gutter journalists, etc. These are the only ones who should be contenders for the sportsmanship award, not the 60% or so (sorry, but 99.9% is an exaggeration) who fairly consistently refrain from doing what they shouldn't do in any case.
The problem that I think you've put your finger on is that most tennis fans - at least most who post on this forum - don't really see the difference, and confuse sportsmanship with their personal feelings towards a player. Consequently, they interpret every action of a hated player as a sign of bad sportsmanship, and every action of their faves as normal or even sporting. That's all the more reason why tennis needs a proper sportsmanship award, so that, maybe in time, people can learn to tell the difference. The rubber stamp that is the current award doesn't do the job.
If it ever gets to the stage where literally 99.9% of players would be contenders for such an award then we can start to worry about Mats Wilander behave-alike scenarios.