I will be the odd duck here and say that nothing you named is easy or hard. Every reptile requires a specific set of husbandry requirements. Some animals are more forgiving of errors in the husbandry but with the great amount of knolage we have about how to take care of various reptiles spot on husbandry is mearly a dollar amount more than anything. You eather take the time to set up the proper home with the proper equipment... i.e. infared temp gun, digital tempature and humidity monitors, uvb lights, proper diet... ect...
So i think its more a question of cost than anything. I dont think there is a cheaper and less time intensive reptile to care for then a snake. I currently have a Chameleon, crested gecko, bearded dragon, and two snakes and the animal that needs the least amount of attention is the snakes. The dragon eats alot and requires attention daily, as dose the Chameleon and crestie.
I would say its a mater of time and money but that is just me. They are all rewarding pets.