I voted for Breanna but, really,
Katie Ledecky seems like the best athlete. She holds three world records and is the current world champion in four distances. Breanna is very, very good but I wouldn't call her the best in her sport or the best power forward.
Of the four choices, I would pick Biles
At the 2015 World Championships, she won gold medals for team, all-around, balance beam, and floor exercise, while taking a bronze in the vault.
Biles is the first woman to win three consecutive world all-around titles (2013, 2014, and 2015). She has also won three consecutive gold medals in the floor exercise and two consecutive gold medals in the balance beam.
In three world championship appearances, she is the most decorated American female gymnast in history with 14 medals (10 of which are gold). She also holds the record for most gold medals won by a female gymnast in the history of the World Championships
World Championship History
2013 GOLD: All-Around, Floor Exercise, Team
2013 SILVER: Vault
2013 BRONZE: Balance Beam
2014 GOLD: Team, All-Around, Balance Beam, Floor Exercise
2014 SILVER: Vault
2015 GOLD: Team, All-Around, Balance Beam, Floor Exercise
2015 BRONZE: Vault
In her 14 competitions as a senior gymnast, she was won the all-around title 12 times (she was runner-up the other two). She has not lost an all-around competition since August 2013, when she finished second.