I don't recommend pee pads. They have an attractant added to them -- an odor that encourages pups to use them. But the pups use them and then go away, while the guinea pigs are on them all the time, with their noses close to the source of the odor.
There is another issue with using the disposable "pee pads"........and one of concern. That same attractant that is put into the pads to lure puppies to them also seems to lure cavies.......and your piggies will chew on the plastic and swallow it. Now the stage is set for intestinal obstruction.
As an example, I had a female who had pea eye and poor vision. But, those beady little eyes could spot that blue plastic and dig it out no matter where it was. I've had problems with my current boys doing the same. I needed a bit of extra absorbency under my liners and tried to hide the puppy pads. One of the boys would root under the liner until he found the pad and pull on it with his teeth until he could easily access it and chew to his heart's content. I finally had to totally stop using the pads for obvious reasons.
Some cavies will use a litter box and some won't. I use a plastic kitten litter box with a layer of
SoPhresh crumbled paper litter (from Petco) and then a layer of hay over that. My boys love their litter box SO much that they sleep in it about half the time. They love being able to do two things at once.......munch on hay and pee/poop. Of course that means that one has to be extra diligent about tidying the box, but my Sparky loves the box so much that I can't bear to take it away from him even though he needs frequent butt baths to keep him clean.
If you do decide to experiment with a litter box, don't get one of those useless little corner style boxes. The box needs to be large enough for an adult cavy to stretch out in. Don't worry about how they will get in/out of it. Mine have been just jumping over the sides since they were quite small.
EDIT: You and I were posting at the same time. We too try to be eco-conscious whenever possible. I have tried all types of litter and seem to always return to Petco's
So Phresh. It is superb at controlling odor and quite reasonably priced for a large bag.