I have a pair of tevas (sandals - the teva sneakers/closed shoes are VERY heavy, not good for the parks) and a pair of keens. I like both, but they are different. I can get a pair of good tevas (with the pieces of rubber to guard your feet from the straps rubbing) for $50 or so. Keens are $80-$100. I think Keens are more comfortable, but I will be wearing both on my upcoming trip.
My strategy is to take several pairs of walking shoes (third will be sneakers) and change shoes every time I go back to the hotel. This way you don't get sore or get blisters from wearing the same shoe repeatedly.
If you want to talk to someone who knows about the shoes, I'd go to REI or EMS or some such store to get the proper fit and style you like, even if you order them online later. Just about any outdoors or big athletic type store will sell them both.
Oh, and Tevas are specifically for hiking/canoeing/kayaking, so are made to get wet and dry and still keep you comfortable!
Good luck!