I really wouldn't suggest the top of the foot, mainly because it won't last very long. The top of your foot is constantly rubbed on by your socks and shoes. Even though a tattoo is permanant it can still rub off a little and not look as clear and nice as you want it. Meaning that you are going to have to get it touched up more often than you would like.

The ankle would be a better better place than the top of your foot. I have three tattoos, one on my hip one on my lower back and one on the back of my leg. The only one that really hurt was the back of my leg.