That's a tough one! If you've got a good couple of months to break in a pair of Rainbows, then do that! But if you can't make that commitment then go w/ Reefs. Reefs will form to your foot faster and are more comfy in the begining, but Rainbows are amazing once you get them broken in (best flip-flop I've ever owned). I made the mistake of taking a brand new pair of rainbows w/ me on a trip to WDW 2 years ago and lets just say after one day I pulled out the Reefs. Last Feb I wore my BROKEN IN rainbows at WDW for 10 days and never had a problem. Happy Choosing!
Oh, and if you're considering the black bottom Reefs, they will soak up water and get squishy...which is something to think about w/ the Florida rain!