I've had the same problem with not getting around to it. I meant to harvest my mint last year, but never did.

I'd think drying it is best and you can use it as a tea or blended with other herbs for a tea.

I don't know what is best, air dry, dehydrated, or freeze dried. I was going to try freeze drying, but I don't know if the vacuum process would suck all of the oils out of it and make it tasteless. You might be better off just air drying it.