I've had to tick hamster because I don't have any experience with any of the others. But really it depends on the person as well as the pet. Eg their age, the time they have and the space available. Hamsters are easy in many respects because they sleep all day! On the other hand they are awake most of the night, their most active time - which is why they need plenty of space in an enclosure when they are so active at night and like to do normally hamstery things like forage, and dig and run.
A hamster isn't always the best pet for a child though - especially if the child is under 9 say, it needs an adult to manage things. But then you could say that for any pet for a child.
A mouse might be a bit easier - they are nocturnal and sleep during the day but I believe they are up and about earlier than hamsters - eg during the evening. They can also climb better (and jump!).