Very difficult to pick top 5. First, what are the criteria? Did this athlete dominate their sport in their prime? Did they have a lengthy career? Did they change the way their sport was played, or force opponents to change to keep up with them? Did they go out on top, or did they hang on too long, which may have tarnished their legacy by losing late in their career? Did they specialize and excel in one area, or were they very versatile? Did they go about their business, quietly being great, or did they seek the limelight?
The person who comes to mind for me is Eric Heiden, the American speed skater from the 1980 Winter Olympic games. I pick him because he won 5 gold medals in distances which had varying physical requirements. Heiden competed and won the 500 meters sprint. This would be the equivalent of say, the 100 meters in track and field. He won the 1000 meters, which could be similar to the 200 in T&F. He won the 1500 Meters, which might be like the 400 in T&F. He won the 5000 meters, which might be like the mile in T&F. And he won the 10,000 meters, which might be the same as the 5 or 10K races in T&F. In each race, he set the Olympic record and set one world record. These races ranged in their physical and athletic prowess from the pure anaerobic, speed and power of a sprint to the pure aerobic stamina of a marathon. He competed across this wide spectrum of events against the best in the world who specialized in each separate race. This feat, in my opinion, far surpasses the decathlete, who competes in 10 different events, but they are almost never the best in the world of any single event in that sport.
It is very difficult to weigh individual success against success in team events. Yes, MJ, LeBron and Kobe were amazing, but they were not successful until they were surrounded with other superstars. The same can be said for Brady, Gretzky (Bobby Orr is my choice for the best hockey player of all time) and any of the great baseball (Babe Ruth, Reggie Jackson) and soccer players (Pelé, Messi, Johann Cruyff). Could they DOMINATE on their own? No, they needed teammates to succeed.
Roger Federer, Steffi Graf, Serena Williams, Tiger Woods all had wonderful runs where they were simply incredible, but each had a foil, who was very close to their success rate and just a step behind them, and took over the sport when they faltered.
Any comments?