pay off first rental property vs down payment on second property

Hello gang,

So this question is probably pretty common. I can pay off my first rental property (condo)for $50K and enjoy a cash flow of around $515 per month or $6180 per year which is around 12% ROI assuming 100% occupancy and zero repairs (which has been almost true for the past 9 years) Or, I could use the $50K on a down payment on a new property. What would you do? My initial thought is that if the new property cash were to cash flow more than $515 per month than that would be the way to go? Thank you for your thoughts and time.