How to address invitations

I have several married couples who do not have the same last names. How do I address their invitations:

Mr. Smith and Mrs. Jones OR
Mr. Smith and Ms. Jones

????

Thank you!

Mr. Smith
Ms. Jones

(on separate lines)

If they were married and had different names, I put them on the same line:

Mr. Smith and Mrs. Jones

If they were not married, they were separated:

Mr. Smith
Mrs. Jones

Definitely, 'Mrs.', though...if she's married, she should have that title.