though both of them have an equal meaning, I think "have a seat" is of more friendly approach and "take a seat" is a bit sounding like a command (it's like "grab a chair then sit down"). :)

romulus is right. "take a seat" is slightly more commanding in tone than "have a seat" which is more like offering a chair. The difference is very slight though.

Add the word 'Please...." for more polite

Hi... Yes the meaning is the same... Don't worry!

i think there is no difference between the two phrases.