I would say it's something like this... if you care about going first then choose Kakuzu, if you don't care about going first then choose Sasori.

If you can put Sasori last and try to make him go last, if he pops his mystery after everyone has moved then they should be paralyzed in the next round. I think he's statistically weaker than GNW Kankuro, and that no prompt mystery isn't going to save him. He would probably do fine with Kankuro because he can heal puppets, but he's kind of bad. I think he's really bad because no prompt on a paralyze mystery and his stat aren't that great.

For Kakuzu you need 60 Chakra and he can prompt, going first, dispel buffs and can cause repulse which starts a chained-chase. He's great if you can get 60 chakra second round and decent third round because he's squishy. It's hard to get him to the third round and it's hard to get 60 chakra by the second round to start your mystery first. He's squishy and dies fast, while also requiring someone else to die so he c*ways start chained-chases.

They're both bad and outclassed by other ninjas, but they still have worth for specific reasons. I have both of them, Kakuzu at 4 stars though, and with Lightning main you already have paralyze so you should go with Kakuzu if you can get his chases to work with yours. (Might need Dog of Hell)