I would scout around some cities/locations that you are fond of and are willing to travel to and check for availability for the times you can travel. I would grab some ideas by going to goldpassport.com and check out the lists of hotels by category...of course starting with category 5 and move down from there (earn 'em cheap and redeem 'em big )...sort by location and availability...and choose from there

I was a bit disappointed just after the first of the year regarding availability in places I was interested in--it seemed good in Dec (before I had earned mine, of course)...availability has dropped off a lot since the first of the year in the places I was interested in (for example no luck for any weekend at the Hotel Victor or PH Chicago)...I was able to get something good for the three free nights I had but availability was so weak (i.e. nonexistant) in places I was interested in that I changed a few reservations for later this month....why earn if you can't burn (as you'd like, at least)