1. It's not my bag.
2. It isn't my bag.

What's the difference between "is not"-form and "isn't"? There's no difference in meaning, but maybe, there's a difference in emphasis? Which form do you use more often?

Thanks for your help in advance.
Okay, Barb, I grabbed your purse for you, so we can go.
Yeah, only -- that's not my purse. -- I'd more more likely to say it this way than "That isn't my purse" because it lets me put more emphasis on the word "not."

Semantically, they're the same.
I've felt that "is not" expresses more emphasis but I wasn't be sure. Thank you for the good example.