@Brandon Pearsons
The math would tell you that as long as you have positive leverage and you can reinvest at the same rate (meaning that your net return is > cost of debt), you should always take the cash flow vs. paying down principal. That being said, I really think you have to balance your desire for the cash flow and to acquire more properties with the benefits of not being over levered. Since I have a day job and am not reliant on real estate to pay bills, I am willing to take more of a risk because if I have a hiccup for a couple of months, I can pay the notes on my properties with income from my job. That being said, I pick cash flow (B/C, not D) all day.
@Mike F. I appreciate your comments, but you can essentially build net worth through cash flow properties as long as you put the cash flow in the right investments. The #1 issue I have with appreciation investors is the fact that a significant component of your model is built on on a forecast (housing price movements) that no one can predict and the average investor is not going to be wise enough to pick the right areas and houses for appreciation (look no further than 2008-2010 period). I am not advocating buying D properties, but the certainty of cash flows that comes with B and C properties (if you have a good game plan) is much higher and more controllable than the certainty of appreciation.