I wore Birkenstocks for years - used to work 5 12's in a row, pregnant and never missed a beat
I didn't do staff nursing for a few years and lost track of where my old Birks got to so I tried a pair of Crocs - felt ok at the end of the shift, but boy, did I pay for it the next morning - the crazier the shift, the worse I felt (I work in ICU)
so.........bit the bullet and went on e-bay and got a pair of Birkenstocks - black ones from the "Alpro" line - $55 out the door with s/h and everything - they usually retail for $120 - I've worn them for a few shifts and I will never look back - threw my Crocs in the washing machine to get all the ICU gunk off and now they are just to kick around the house in...........
unfortunately, sometimes you have to try a few things to find out what's best for you - gets costly but if you find what works for you, it will mean you aren't hobbling in your retirement years!