I've heard there is a big difference in Goodyear Marathons and everything else. I personally don't believe it. The biggest thing that kills tires are bad axle alignment and the sun.
Tires have a compound in them that resist drying out. However, it only works if you keep moving the tire. Rotating and flexing brings that compound to the top of the tire. Which why tires dry out if they sit still for long periods of time. Keeping them inside makes all the difference in the world. At least cover them or keep them out of direct sun. 16 years is impressive.
Personally, I'd take it to Discount Tire and get what they have. They move tons of tires and have the best customer service in the industry. That is what I did when I replaced mine last year. No problems.