Is it ALWAYS best to put least amount down?

[Anthony King]

What is the best way to compare mortgage options if the down payment and interest rate are dissimilar? I know a lot of people say to put the least amount of your own money into the deal as possible, but that can't always be the case.

For example I have two commercial lenders who have approved my purchase on a 16 unit multifamily.

Lender A wants 20% down, 6.6% interest on a 20 yr amortization.

Lender B wants 25% down, 5.91% interest on a 20 yr amortization.

Do I look at IRR or ROI at some point in the future to compare the two? Or something else?

If the 20% down option had an 9% interest rate, you'd probably be better off with the 25% down and 5.91% right? At some point the higher rate stops being worth the lower down payment, but how do you know when?

Thanks for the help!