Considering sakura and chiyo could beat sasori, I am going to go with gaara and oro being stronger.
1. They were the best available combo against him. If any of them fought him alone, Hiruko puppet would be enough to own them. Chiyo had nothing in her arsenal that would be able to destroy that puppet, thats why she had to use Sakuras strenght.
2. Considering that 3rd Kazekage was the strongest of all Kazekages, he could use IS in same quantity Gaara and 4th Kazekage were using their version of sand.
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Sasori has all chakra and skills of 3rd along with human puppet made out of him. Sasori has only gotten little more serious with IS when he used Satetsu Kaihou.
3. Considering that in the end Sasori let himself be killed, he had no will to live at that time.