rental property investment criteria

to me criteria for ranking rental investments opportunities between different areas can be understood by looking into the components of the net rental yield:

• rental gross income
• vacancy rate
• expenses, local and state taxes

rental income and vacancy rate evolution will be influenced by demographics: whether population increases and how median income moves. So I would look at these fundamental data rather than just see if prices have increased year on year (which just indicates the gross income is getting worse)

Would you add any criteria?

According to you, where are the best rental yields (both bet yield and potential increase) in the US?