Many in the sanitation treatment industry feel the garbage disposal was among the most troublesome inventions in the history of the modern home. Treatment facilities are designed to remove bacterial and viral contaminants, not solid wastes (grinding it and sending it into the sewer system does not change the fact that it is solid waste). Most plants have been retrofitted to remove the increased volume of food waste (among other things), but it is no where near as efficient as composting this waste stream.
Essentially, using a garbage disposal is another way to outsource waste removal without paying additionally for it, and it puts an undue burden on infrastructure. To see this process in action, and to see what happens when food waste is co-mingled with wastewater, I highly recommend taking a tour of your local treatment facility - usually this is a free service provided to citizens. For example, if you live in southern California, the Orange County Sanitation District and Los Angeles County Sanitation Districts will offer free tours:
Composting is relatively easy, although it does require a bit of maintenance. If you have a backyard, outdoor composting is definitely the preferred solution - there are plenty of websites out there that will provide instructions. If you live in an apartment or have limited space, consider worm composting. If done properly, there is no odor, and the end product (worm casting "poo") makes for perfect potting soil.
Composting (as above) should only be done with specific kinds of scraps - e.g. fruits, veggies, breads, egg shells, garden cuttings, etc. Do NOT add fats, oils, meats, or dairy products.
I had never heard of guinea pigs as a disposal method - cool idea! Along those same lines, many people in the U.S. are using chickens to achieve the same goal. Chickens will eat anything, including meats, fats, dairy products, cooked food, etc! But check your city or county ordinances to make sure this is approved in your area.