I have always found the mascot for the Oakland Raiders to be very interesting. It is basically just a football player. That is like being called the Oakland Football Players. Ok, so maybe it isn't that stupid, but it is still an odd logo. Being so odd is what also makes it so iconic. Like it or not, once you see black and grey, you can't help but think of the raiders. Their normal helmet is a little too classic though.
The top right is exactly the type of modern design I would expect to work well in the NFL in this era. It has the big logo with a carbon fiber background, looking very sleek. The bottom right has some great ideas, but the texturing is a little too much. It makes the helmet appear dirty.