Everyone seems to forget that Sasori had at least 250+ other puppets which he probably kept with him on scrolls. Thats a bitch load of unique weapons and I bet he had different puppets to counter different situations. Dammit makes me even angrier that Sasori had to die premarturely I don't think we saw enough about him to justify killing him off. We never learnt his backstory or saw any of his more interesting puppets. I hope kishimoto can revive him with dues-ex-machina-no-justsu. Another interesting thing to consider is that Sasori was not so much defeated as much as he let himself be killed. Chiyo mentioned that he could have avoided the final blow but choose not to.

Keep in mind Sasori also had henchmen as well. Only difference is that we never got to see what they could do. Ultimately I see sasori as the winner simply because he dosen't have the biological limitations as Orchimaro. I mean technically he's a cyborg right? Meaning he dosen't suffer from fatigue. Plus all of his tecniques are carried out mechanically by using the chakra strings, he really dosen't need to put any of his chakra into his tecniques he simply carries them out by operating the puppets. Sasori's whole fighting style is compltetly unconvention since everything he does has been previously manufactured by himself as opposed to aquired. Dammit human puppets just kick ass so that's why I think he'd probably win. Besides he is the legendary Sasori of the red sands. Since he's got a title that means he's easily on par with the sannin or of the same calibur.

Don't estimate diadara I think that we really haven't seen everything that he is capable of. Reason why he respects sasori more is that my guess is unlike diedara who most likely has a blood line limit everything that sasori does has been made by hand and constructed by his own intellect as opposed to relying on skill. In the greatest sense sasori is a genius artists more so then a skilled fighter. Sasori was like the lex luthor of naruto literally compating his opponents with the machiniations of his mind.