When it comes to this topic, there is a rule order to the smart rules you have in place.
In the case your contact or visitor meets the criteria of more than one of your smart rules that you have put in place, that contact/visitor will see the content from the rule which comes first.
Please note that rules are read from top to bottom, as when you make something smart and add a new rule, this new rule is placed at the bottom of the modal, which places it last within the hierarchy.
Take a look at the screenshot noted below - The highlighted rules will show different content to contacts that are members of the lists Smart Rule #1 and Smart Rule #2.
If a contact happens to be a member of both lists, the contact will see the content from Smart Rule #1 because that rule comes first.