I agree that cash flow is the best. But not always possible, and maybe not the best option. Just for another perspective, I have held multiple rentals for a decade. One of them for years did not cash flow--I paid early on up to $500 out of pocket each month. Now it does cash flow (maybe $100). However, the main point is that mortgage has been consistently paid by renters for the past decade. And it has gained about $100,000 in value at the same time. By the time we have paid off our current mortgage (another 8 years), we will be able to quickly finish the rest of that condo mortgage off, and will immediately have a monthly income of $2300 or more from the rent off of that condo alone. Forever.
What you need to think about is, if you sell, do you plan to buy another investment property or just pour the money into your next residence? If you sell in favor of just a residence, you will be lacking in a very good solid investment. How do you plan for retirement income? If you won't live too far, and have the ability to manage it yourself (which I do), you will find that a rental that pulls in $2400 per month can be a great source of income for your future. While you pay off your primary residence, someone else is paying all of your interest, condo fees, and most of your principal on another property. I would keep it unless I had a far better investment property available in front of me. Don't forget, every sale and purchase has transaction costs. You've already paid those, so what you sounds like a solid investment.