Is blitzcrank or thresh better in a teamfight

Thresh is generally better for teamfights and Blitzcrank is better at making picks.

Thresh has the potential to apply a massive slow to most of the enemy team, pull or push them all away, hook one for some brief cc and also pull in allies for strong engages.

Blitzcrank can at best get an AoE silence off and run around trying to pull people.

Thresh is better all around. Blitz has a q, that's it. Thresh has a q that snares for longer, a flay to follow that up, then an aoe slow to follow that up. If your adc is in trouble you can lantern them out, which also gives a sheild. Blitz you grab, knock up, ult, but hey your support, so they flash away. Thresh can flay them back

Thresh is usually better. Against squishier teams, Blitz will be superior simply because he can disable a carry and almost kill them at the same time.