Samba's. And to disagree a bit with the guys who say these aren't good for workouts: I played indoor soccer for a few years and always wore samba's. They didnt' seem too bad at all - grippy and fair levels of support. Maybe my arch is a bit lower than most, but I had no problem using them for athletics.
from someone who owns 40 pairs of sneakers at the moment and has owned over 100 others, i think the most comfortable shoe I have is New Balance 577. Next is Air Max 90. Also Air Stabs are really comfortable but not as common.
But for just walking around, I find a perfect fitting leather dress shoe to be just as comfortable.
Out of those three I would say Purcells. I hear the CPs are pretty comfortable. I love my vans, but I recently picked up my first pair of Purcells and I have to say they're softer on my feet (although they're a little tight on the sides due to my wide feet).