Aruba
I don't think "request first" will diminish your chances, but beware ... I learned the hard way. If you do a "request first", you can only exchange up to the date of your assigned week (and if your assigned check-in day is Friday, that means you can't exchange for Sat or Sun of the same weekend).
So ... if you get a week assigned, make sure it's way beyond when you want to exchange for ... e.g., get a late August week and do a request first for your dates ... but you have to be willing to go to NCV that late August week if your exchange doesn't come thru.
Unless they've changed the rules ... this happened to me about 3 years ago, I was able to talk Marriott into cancelling my request first and I just did a real exchange.
Aruba is outside of the hurricane zone ... that's what's so nice about it. You might get some residual rain but nothing hurricane-force.