你比大家都聪明。 都 describes a group, so it should follow a group. Here 大家 is a group, so 都 should follow it.

Both are good, but they do not mean the same thing. For example: this expression "你比大家都聪明" means you are smarter than everyone else whereas 你都比大家聪明 means that person knew you are smarter than everyone else. Let me give you an example: 你当然可以做到 因为你都比大家聪明. The word"都“ act as an emphasis in this sentence. I hope this helps. Have a good day.

the first one

你比大家都聪明 大家都比你聪明 focus on 大家都 大家 means all persons, 大家doesn't mean everyone,大家是复数，everyone是单数 ”你都比大家聪明” 的“都”是让步的意思，它的下一句是“大家还笨得了吗？大家一定更聪明”，它隐含着的意思是“像你这样的笨蛋 都这么聪明，大家这些聪明的人一定更加聪明了”

The first one