It depends on a number of things, including your goals, risk tolerance, time to ER, etc.
It sounds like you're in a stable position now, with 7/8 properties cash flowing (though I don't know what you count in "expenses" in your cash flow explanation, so it may be less than you think, but either way it sounds like you're okay).
So based on that last paragraph (the comment about getting to a level you're comfortable with), it sounds like your goals are higher than than your current level, so that indicates to me that you may want to go ahead and buy that one (or more, or whatever) property a year for the next few years before you accelerate the payments on the rest.
Assuming your new property purchase has a higher return than the interest rate you're paying, of course. Otherwise you'd want to pay down first before buying new ones, mathematically.
Start with your end goal (where do you want to be in, and in what time frame) and work backwards to what you have to do to get yourself there.
Welcome to the forums!