I say turkeys, at least where I live. Deer really are not that smart and really don't see that well. They hear and smell great though. The biggest thing with deer is they are very alert and on edge.

Turkeys are actually fairly smart I think and like said can see incredibly well. You really need good cammo for turkey and be able to sit still. Not to mention they are sort of hard to kill. They are tough as heck! I kill at least one deer every year but have yet to get a turkey. I came close a few times though.

The pay off is much better with deer though. You get quite a bit of meat with a deer and the prestige seems to be greater. Turkey hunting is simply for the challenge and sport of it. For what it costs to turkey hunt you could buy two or three at the market. I would also agree it depends on where you live. Some states have quite a few turkeys and pretty liberal laws to hunt them.

If you want a challenge I have heard that Prong Horn and large cats are pretty hard to kill. Prong Horns have all the senses of a deer plus they can see VERY well to boot. And cats are natural born hunters themselves, so chances are they are better at it then most humans.

My opinions anyway.

Paul