Personally, I would be thinking more about where I wanted to go and less about trying stay at the highest cost hotel possible. While I like a top-notch, expensive hotel as well as most others here, I also like to do and see things where I'm staying. And that is usually more important to me for the overall trip.

So the real question may be more about what you want to "do" or "see" during your trip? Do you want a beach vacation? Mountains? Skiing? Big City? Where in the world would you like to travel? Figure that out, and then find the best Marriott you can in that area and see if you can use your points there.