I hate that argument of ''Sasori died to an old lady and Sakura''. Have you guys ever honestly thought about it? Of ALL the people present in that mission to retrieve Gaara, Chiyo and Sakura were literally the perfect combination for defeating him. Honestly, if Sakura/Chiyo and Kakashi/Naruto switched places.. I think all four would be dead (excusing plot-no-jutsu of course).
I think Sasori would beat Orochimaru.. but I'll make a short analysis.
Orochimaru - Snake jutsu, regeneration, sword of Kusanagi, Soft Physique Modification, Rashomon, and Edo Tensei. Edo Tensei is the big hitter here. With Edo Tensei, Orochimaru can revive practically anyone who hasn't had their soul stolen.
Sasori - Human Puppets, Poison, and Information. Sasori knows a lot about Orochimaru from working with him. On the other hand, I pretty sure Orochimaru doesn't even know Hiruko is a puppet. Hiruko alone can launch huge volleys of poisoned needles from his arm and his mouth, and has a poison-tipped tail. Then there's the Third Kazekage puppet, with poisoned Iron Sand. On top of that, Sasori has 297 other Human Puppets, 100 of which he can use at a single time.
Orochimaru has poisonous snakes... Sasori can't be poisoned. Sasori can fill an entire area with poison gas... and he can stand in the center of it. A scratch or a mere sniff of that poison.. and Orochimaru is done for. Orochimaru DOES have an immunity to basic poisons.. something he taught Sasuke as well. However, I find it extremely unlikely that Orochimaru would be immune to Sasori's poison. The method of becoming immune to a poison, the way Orochimaru does it.. is by ingesting non-lethal doses of that poison over time. Sasori's poison is lethal at a mere scratch. Just a scratch. How are you supposed to take non-lethal doses of something that kills you if it just barely enters your bloodstream?
And.. Sasori's not good at Taijutsu? Excuse me if I'm wrong.. but isn't Sasori a living weapon? He has one weak spot.. one spot where he can take damage.. and even then.. he can quickly replace himself into another puppet. In my opinion.. Sasori outsmarts, outnumbers, overpowers, and is just far more lethal than Orochimaru.
There is no room for error in fighting Sasori. None.
Side-note: This is a highly debated subject in a lot of places.. but there's a possibility that Sasori is immune to genjutsu. You can say that because he lacks a nervous system.. his chakra can't be disturbed by Genjutsu (Genjutsu assaults the seishin (mental/spiritual energy) of the target through the nervous system, from what I've learned). But you can also say that if Sasori didn't have a nervous system, how would he sense things? Sasori has a seriously hax'd body.