Both come in several styles, and both are highly regarded on the DIS.
A few things I look for are good support, adjustable straps, and a strap around the back of my ankle (as opposed to flip flops)
Another important thing for me is making sure my toes are protected. Either that they are a bit covered- like most Keens- or that my toes are not too close to the top edge of the shoe. Plenty of times while I was wearing sandals, I've had my toes smacked by a door, stepped on, or hit by a wheelchair/stroller/roller bag/etc. (folks back up all the time without looking!)
If my toes get smashed bad enough, it makes for painful walking at WDW.
I really like the three strap Ecco sandals.