Strongest: Gaara, A, Mei, Oonoki, Tsunade.
Gaara is fast (on sand), can fly out of most people range, have a large stamina, can create a huge sand tsunami is little to no time, and his sand is strong enough to tank C3 which blast is comparable to a tbb and can block 5 of Madara's Complete Susanoo blades.
A is the fastest of the 5 and have chakra on Bijuu level. He has the strength to kill most people he hit and have the speed that even a MS user can barely see. Have a high durability and doesn't react to pain as others would such as not showing signs of Amaterasu burning him or cutting his own hand off. His anger can cause him to be narrow minded though.
Mei can use fire, water, earth, boiling, and lava jutsus so the ways she can attack and defend can vary greatly. Her village specialize in the hidden mist jutsu so she can hide her presence while attacking her opponent, would be bad if she also mixed her boiling mist as well to melt her opponent and even worst if they breathe it in. She can spread lava around the battlefield to limit her opponent movements.
Oonoki would come next, many people put him as the strongest ones and yes he has the strongest attacking power but many of you are forgetting that Oonoki suffer from his old age which can cost him the fight. Look at Oonoki from when he was settling off to the Kage summit, his fight with Edo Muu, and Edo 2nd Mizukage where his back would give out. He had the alliance or other Kages with him to help him when he suffered back pains but if he's fighting someone who is top tier the being able to his his target wouldn't be easy and dust release cost a lot of chakra and has a charge up time. He does have access to his earth, wind, and fire elements but he mostly stick to earth or dust.
Tsunade being last since she requires herself being in close range and the other Kages can either fly, move faster than her, or hide their presences/fill the field with lava. Her Yin seal healing limits her life span as stated by Shizune in part 1 since the cells can only reproduce ever so often.
