If yokozuna Onosato had a healthy left shoulder he would be the best. He can beat all the others reliably, only failing a couple times per basho. But he is injured so he sucks.
All the other top rikishis, inlcuding yokozuna Hoshoryu has the tendency to fail against opponents they should beat. Hosh is barely better then the rest.
Aonishiki, the young Ukrainian, is really promising, he is strong, quick in action and thinking, has good instincts, he really has a talent for this. However he relies a lot on bending forward from the hips, almost horizontal, and they started to counter that, plus when his back fails, he'll be buggered. But by then perhaps he'll be yokozuna for years. He is ozeki now, which is the topmost rank just below yokozuna. My problem is that I suspect they stack the deck in his favor. Just the other day they let him walk with an obvious hairpull, which is one of the rare forbidden moves.
Atamifuji is also a young talent. And he is big. He rises slower than Aonishiki, but he might become even better. Time will tell.
There are some more young talents, but they need to mature.