Last spring, I took a pair of Keen hiking sandals (stretch straps, Teva flipflops (the thin ones), a pair of Keen flipflops with the toe protector and some plain zori sandals. I was in Playa for six weeks. Also, I am shoe crazy. I really like the Keen sandals for walking around ruins etc. This shoe has nice traction and dries fast. They were great for climbing the main pyramid at Chichen Itza. The only problem with them is that if your feet have the tendency to swell like mine do, you will be miserable. If not, then these are great sandals. The toe protection is great expecially if you are wading in rocky areas.
The Keen flipflops were a painful experience; they are not good for walking. I got blisters on the bottoms of my feet. I wore out the Teva's. On that trip, I missed my Chaco sandals. The straps are adjustable; this is a great feature for when my feet become inflated. In May, when I return to PdC, I'll take a pair of Chacos and some flip flops.