Gaara wins mid-difficulty, IMO armor of sand makes it very hard to give Gaara any surface wounds / injuries that break the skin and draw blood (how puppeteer poison is comonly spread.)
Chiyo will survive much longer than Sakura, if Chiyo controls her with puppet strings like she did against Sasori, then Sakura may have the agility to avoid sand coils and sinkholes for a while, but this is at the cost of part of Chiyo's attention on controlling her instead of her usual puppets to defend herself. So essentially Chiyo would be sacrificing her own survival rate to boost Sakura's it won't make too much difference.
Sabaku no Gaara wins.