I've never had a guinea pig, but ferrets have a lot of personality and love to play.
From another contributor:
I have liked my ferret a lot more than when i had a guinea pig
From another contributor:
I have three guinea pigs and one ferret. I myself like guinea pigs better. Reason being they are less hyper. My farret is diffiicult to leave alone, he gets himself into so much trouble. The smell of their poop is horrible and when they do have accidents, the carpet gets stained and the smell of poop is left in the carpet. Maybe this is because my ferret is young for the most part, but he is a handfull. A ferret will be a ferret no matter what. So your chances of getting one that is calm as a baby are slim to none.
Guinea pigs are nice because you can leave them home alone and wont have too much to worry about where as a ferret, needs to be let out of their cage a couple times a day. Ferrets are smart but they are so stubborn that they will do the same thing they got in trouble for again.
Don't get me wrong I love my ferret but if your the type of person who doesnt want to watch an animal every moment they are out of the cage, then I wouldn't recommend a ferret. If you like that kind of thing however than go for it.
Guinea pigs all have different personalities so it depends on which one you end up getting. I have one pig that is very protective and is the leader of the group he will sit on top of his house and watch the other pigs play. He also sits on top of his house when I vaccum so he can watch me. This pig is very smart. He knows how to get his way. If he wants a certain vegtable, he will turn his head to any vegtable I give him until I give him the one he wants, while the others will be more than happy to eat whatever I give them.
Another pig I have loves to be pet. He loves his belly rubbed and will lay on my stomach for hours without pooping or peeing. I've acctually never had this pig poop or pee on me or even bit or nibble.
The third pig I have is sort of skiddish doesnt like to be pet too much but maybe that's because when I take him out of the cage the pig leader calls for him. The pig ends up paying more attention of the leader calling him than me paying attention to him. This pig is the healthiest looking pig you ever seen.
One thing I want to point out is that when having a pig, they can have littlle things go wrong that might leave you in a vet office. If hay gets in their eye or cuts them than you will end up spending more at the vets office than what you paid for the pig in the first place. They seem like cheap animals but if your like me and spoil them, then it can be expesive. To me my ferret is less expensive than my pigs. That would be a plus on the ferrets part.