Different fellowships have different policies when it comes to both deferral and the number of times an applicant is allowed to apply. Contact both organizations and find out the exact implications of not accepting the offer at this time. This simple element may quickly sway your decision in one direction or the next. In the best-case scenario, you may be able to have your cake and eat it too, perhaps accepting one fellowship after the other has run its course. Is there a way that this is not an OR decision, but an AND path?