I've had lots of guinea pigs, and I'd suggest a hamster instead. Being smaller, they don't poop as much . . . which means significantly less cage cleaning and less bedding to buy. I had two guinea pigs, and their cage needed cleaning twice a week (the other poster who mentioned that guinea pigs like friends was right). On the other hand, a hamster only needs its cage cleaned every two weeks. The cage takes up more space in the house. Also -- in my experience -- hamsters wet less while being held.
Either makes a great pet, but I think the hamster is much less work.
If you get a Syrian hamster (it'll be a "bear" -- teddy bear, panda bear, black bear, honey bear, etc.), it'll want to live alone, and it'll enjoy interaction with people. They're also the larger, slower-moving hamsters. If you get a dwarf hamster, it'll never be the cuddly thing that a Syrian will be, but it'll want a ham-friend with which to live.