The loans evaluate the property's ability to pay the principal, interest, taxes, insurance, etc. from the rental income without considering the investor's separate W2 wages. 

I would talk to the original lender before you make any principal payments.

If you have good cash flow on your properties, there is an argument to kill some of the debt with high interest of high K factor (large principal, small interest payments).

@Agustin Rossi  The Home Must Be Your Principal ResidenceTo qualify for the exclusion, you must have used the home you sell as your principal residence for at least two of the five years prior to the sale.

Do you look at the annual average principal amount of the loan paid down over time?

I personally like the lower monthly payment because you can always make an extra principal payment a year and knock down the life of the loan anyway, but you're not obligated to the higher payment. 

Quote from @Arthur Schwartz: From your PITI, how much is the monthly or annual pay down on principal? 

I opted for the fixed rate with principal payments.

For primary residences, lenders typically don't require PITI (Principal, Interest, Taxes, and Insurance) reserves beyond the down payment and closing costs.

I have paid the principal down to about 179k.