I like people who aren't serious. I like people that have a sense of humor. What's the difference here? Are you asking about the difference between saying I like people who... and I like people that...?
If you are, then the major difference is that saying people that is considered more informal, casual
But if we have to choose between that and who for persons we choose on any rule ?? as example I'm looking for someone ........ I can go on vacation with . here can we use who and that but i'm confused when we use this and this ??
1. I'm looking for someone whom I can go on vacation with. Formal. 2. I'm looking for someone who I can go on vacation with. Informal. 3. I'm looking for someone that I can go on vacation with. Even more informal.
There is no grammar rule about this. Native speakers will use either 2 or 3 without thinking, and probably pick 2 more often than 3. You are safest going with "who"