Pigs are fabulous...I had some in college. They do stink though if you don't clean the cage out frequently (a few times a week or every day even).
And yes, they purr...or rumble, whichever you'd like to call it. It's great.
They can get pretty big. I've seen them almost as big as a small rabbit.
buy a big "hamster ball" for them but you shouldn't because their backs are designed for that kind of bending. It can hurt them. Instead, get a playpen, something like this:
Put some newspaper down (the pig will chew it but as long as it's black and white they'll be fine) on a hard surface and let them run around like nuts, wheeting and squealing like little pigs. The sounds they make are great too.
They are also prone to upper respiratory infections. Whch is what one of mine died from. The other, I honestly think, died of lonliness. She missed Juliette terribly.
Other than that, the tend to not bite much but will if they get really scared. They don't like to be held while you are standing for some reason...fear of heights I guess. They like to be cradled in your lap.
Peruvian guinea pigs are the long haired ones...so cute but you have to bath them more often as they pee on themselves and their hair gets icky. Pigs can swim, did you know that?
One of mine loved it and I'd fill the tub up just enough so she could swim if she wanted and there'd be a rock on the other end for her climb on if when she was done. Funniest thing ever.
Their food can get expensive since you need to provide roughage (timothy hay is an absolute favorite) plus the pellets and then some fresh veggies now and then. But if you buy in bulk, it saves you money.