I wore a combination of Clark's athletic sandals (I'm sure very similar to Tevas), Birkenstock slip on sandals, and Crocs for a weeklong trip last October. I only got one small blister during the week- I was wearing Crocs with socks, and it rained on us. The wet socks rubbing on my heel gave me a blister, not the Crocs!!
Clark's- great, very comfy. Only problem- they didn't do well in rain. The liner is suede, and when it got wet, it was not fun. Then, they didn't dry very fast.
Crocs- great!! I thought my feet would sweat and slip around, but they didn't. I liked them with or without socks- just didn't like when the socks got wet. Obviously, Crocs are great in the rain, since they don't require any drying time- just wipe off with a paper towel, and you're good to go!
Birkenstocks- usually, I love them and wear them all the time, but I discovered they didn't work for me when walking long distances. My feet got SORE after a full day on them.
The one thing I did that I learned on the DIS: put deoderant on my feet each morning. Usually I get several blisters, but aside from the one from the wet socks, none on this trip! I also used peppermint foot lotion each night before bed. The old tootsies held up pretty good for the week.