In order of easiest to hardest...
Epcot- In Future World everything is open and easy to find. Large walk ways and informative signage point you in the right direction. World Showcase can be a challenge if it is crowded, but most times it is fine.
Magic Kingdom- It has the best overall plan (hub and spoke) but for me it loses points because the walkways aren't large enough. The park could benefit from some side walk widening and better traffic flow management.
Hollywood Studios- The walkways are large enough, but there isn't a very logical way to work this park. It is full of dead ends and roads that don't connect effectively. It is very easy to get lost in this park. The amount of back tracking one must do to get from place to place is tiring.
Animal Kingdom- Even though this park is based on the hub and spoke idea it lacks everything else needed to make it effective. The walkways are jagged, narrow, overly bumpy, and full of unnecessary inclines. There are few open areas and there is no way to get from one land to the next without walking all the way back to the center of the park. Even when the park is only minimally busy it still feels like chaos because people are running all over the place. I feel like in the case of this park they got carried away with the themeing and it overtook any sense of organization and efficiency there might have been.