I'd do the AA Plat Challenge in any event; and if you can think of pulling off 100k miles or points -- points on higher fares are 1.5 points/actual mile travelled -- then I'd aim for EXP. However, if EXP is not readily achievable, I'd diversify and put my eggs in at least two baskets. (And also keep in mind the geographic benefits of using foreign frequent flyer programs and/or basing an account in an easy-to-achieve-status country for one of those programs.)