Everyone's feet are different. What may be comfortable for one may not be good for another. A lot of factors come into play, like weight...if you are a larger person, you will need sturdier shoes with more support. If you have bad knees, hips or ankles, a shoe with air cushion and full foot support is what you need. Really good sneakers...not old worn out shoes are your best bet. The new breed of sneaker needs no break in period. They offer support and protection.
Sandals are nice and they look comfy...but for the long haul (for me) sneakers are the way to go. On my last trip I brought a pair of Mephisto sandals, which are one of the best made sandals ever. I wore them 1/2 day and that was it. I wore my sneakers, which were new, everyday...and we do 3 parks a day!..No problems, no blisters, no tired feet or sore knees. I prefer the Saucony Hurricane 7....an unbelieveable shoe. Light breathable and full support and a full cushion of air. I wear this brand all the time for working out (I walk 4 miles a day 5-6 days a week) And I replace them every 5-6 months.