Having owned hamsters, guinea pigs, and gerbils, I'll vote HAMSTERS every time. Random thoughts:
Always choose a variety that has "bear" in the name -- honey bear, teddy bear, black bear, panda bear -- because these are Syrian hamsters. They are larger, slower-moving (read: easier to catch), and they like to be petted. They are less likely to bite, and they prefer to live alone (no need for two hams, no babies to give away). In contrast, dwarf varieties are FAST (like gerbils), and they prefer each other's company to human friends.
Their cages do need to be cleaned out every week, week and a half. I strongly recommend Carefresh bedding; it is a little more expensive, but VASTLY superior to anything else I've used for odor control. In contrast, a guinea pig's cage needs cleaning 2Xs a week -- more expensive, more trouble.
When we clean our HamFriend's cage, we give him several scoops of seeds, and we don't think about food between cleanings. He never eats it all, but as soon as we put in fresh seeds, he immediately runs over and scoops up all his favorite seeds -- he hides them in his bed and sleeps on top of them. Greedy little thing.
The cage will cost about 5-6 times as much as the hamster himself.
Get a hamster as young as possible, and pet him gently every day -- give him veggie treats too (pretty much anything except potatoes and tomatoes). He'll learn quickly learn to love interacting with you. Never pick him up with food smell on your hands -- those are the only times we've been bitten. Advice we read in a book: When you first get your hamster, sit (fully clothed) in a dry bathtub (close the drain) and let the hamster run all over you. He'll become accustomed to you, but he won't be able to run away from you. My daughter did this for HOURS when our hams were new, and they're exceedingly docile little critters.
NEVER let your hamster get wet; they cannot regulate their internal body temperature, and they may die. They are clean little things. They spend hours grooming themselves, though now that we have a long-haired boy, we do brush his hair occasinally -- he gets matts.
I wouldn't get a hamster for a child younger than, say, five. The child would be likely to squeal and scare the hamster or squeeze him. When my nephew's over, we hold the hamster for him and emphasize, "Pet with one finger".