@Andrew D.
Not that my advice would be early loan repayment, but I think if you do decide to go that route then which loan to pay off early really depends on the rate and remaining life of the loan, and not the overall size of the loan, if you're looking at reducing your monthly debt payments. Longer life loans with higher interest rates should absolutely be the ones targeted first, all other things being equal (such as early payment penalties, etc).
I'm actually in a somewhat similar situation, but instead of early payment my strategy has been to stagger my loans so that they'll get paid off at different times. Why I chose this approach is because I've found different banks and financing options have offered preferential rates for different tenors at different points in time, and so I've been targeting the best rates available that fit into my investment strategy and keep me cash flow positive whenever I'm looking to finance a new investment.
For example, I currently have loans with 10, 14.5, 22, 23, and 28.5 years left on them, each one getting me the best rate I could get for any tenor via the financing options I used. My larger loans have the longer tenors to maximize my cash flow in the interim, and the shorter tenor loans are pretty much cash flow flat, with the idea being when the first loans start getting fully paid off then my cash flow should begin to increase every 5 years or so. This is also assuming I hold all of these properties for the entire life of the loan, which is absolutely up in the air still at this point. But with what I do have the plan moving forward on any new investment property loan would be to max out the tenor (30 years) to maximize cash flow in the short term - assuming the 30 year rates available make it a good investment.