in the long term muu was always going to win. unless gaara could somehow knock him down and crush him. onoki was losing the dust duel due to his age. rocky terrain is greatly to onokis advantage however. mu can use earth release to raise the earth so that yondy is up in the air with them. of the four, only yondy cant fly. imo without 4th going all emotional and narutos arrival, the two kages were dead
Well Onoki and Gaara make a better team than Mu and the 4th Kazekage.
Gaara>4th Kazekage, Onoki<Mu. Keeping this in mind this battle would be a very close one. Also Mu did extremely well because he was an Edo with unlimited chakra but he is still the stronger of the three in this match up.
It all depends on how much pressure Gaara's dad can put on Gaara because Onoki will need Gaara's help such as the sensing ability in order to defeat Mu. Maybe Gaara can send a couple of sand clones to help Onoki out. While Mu is forming the jinton cube, Gaara can restrain Mu's hands allowing Onoki to finish Mu off. The problem is that Mu is a sensor so his ability to avoid attacks is much higher than that of Gaara's or Onoki's.
For now since it took three kage level ninjas to beat Edo Mu in the manga, I'll go with Mu's team high difficulty.