Based on the two participants' fighting ability, it appears that Doflamingo has the upper-hand and is someone who has a lot of endurance and stamina. When I look at how Luffy and Law vs Doflamingo, the two boys had an extremely hard time battling and Law almost lost his life to his enemy. All thanks to the many helpers (in various extent - little bits and pieces, moderate and more significant help) who had assisted the Luffy team in every possible way for them to win over the kingdoms of Dressrosa and Tontatta. In fact, it was like every single person in the country (citizens, royal families, pirates, fighters, gladiators, straw-hats, allies, etc) was involved in rescuing the country from the evil hand, Doflamingo (the country's one and only enemy, with his crew).
In the Dressrosa arc, Doflamingo had displayed, in every way, superior in his physical and mental capability. This guy has had been through a lot of trials in his life since he was a kid and he has vast experiences in fights and battles, till now. He is in his 40s, which also means that he has more than 30 years of experience in life. I can't imagine what kind of life he has been through, but one thing I do know is that it isn't a life an ordinary person could endure and should go through. Perhaps someone who has gone through war could be able to appreciate the hardship better. But I believe this is the closest I can imagine when I compare it with our modern events, such as first and second world wars. What I'm trying to say is hardship can mold someone's character and even personality, and through the difficult experience, one's endurance and perseverance could stand out prominently. Perhaps the same could be said about Sabo too. But he was fortunate to be found by Dragon whom I think, isn't a tyrant caregiver. As such Sabo may not need to endure as much hardship as how Doflamingo had. Moreover Sabo is still very young and inexperience, while his opponent is an evil king who had ruled a kingdom for 10 years and would not hesitate to kill anyone and anything. When I think about how he used his DF to manipulate the former king, Riku, to kill his own people is enough to say of his cruelty. When faced with someone who has so much anger, hatred and filled with such strong killing intent, it is as if Sabo is facing the devil himself.
We all know how much and how far extent Doflamingo can fight while he stood confidently without giving up, while holding on to his "birdcage" and continued manipulating it. Even after his defeat, his spirit of endurance stood still with him. For a second, if he is given a second chance, I suspect that he would win this time. He is someone who thinks fast and his mind is agile as his physical movement, and he probably would have already thought of a new strategy to win the battle. It seems like this tournament is his second chance!
As much as I would love to see the "good guys" holding the trophy, but for the sake of fair analysis, I would have to say that Doflamingo would win this tournament.
Your thoughts?