I think idiot is a stronger word.

I don't like being called an idiot and I get really upset/emotional when I do get called an idiot because I always feel that I can't do anything right and I feel pathetic

TBH I think both are really grade school level insults. Like the kind of stuff you'd say after running out of good ones. So neither bother me that much. I mean really; nothing says, "you won the debate." like a "ur dumb" or a "fuck you" or (now here's my favorite) a "ur ugly."

I don't necessarily like being called either but I feel like 'stupid' is simply used in certain moments when i fk up on some things whereas 'idiot' is more as implying you lack any form of intelligence overall.
But like zanhar said neither actually affect me since they're both p immature insults (at least imo)

I am an idiot but I'm not exactly stupid :v

I get stupid way more, I'm used to it.

I hear idiot when i do or say something stupid in front of my friends.