I've been doing some research on this topic, looking into a lot of things about Guinea Pigs (cuy) vs Rabbits, which we already have. Here's what I have learned so far:
Cuys have a gestation of 2 months, then 4 months until butcher size. So, from breeding, you have 6 months to plate. Rabbits are 1 month gestation, 3 months to butcher size, so 4 months to plate.
Cuys have average 3-4 per litter. Rabbits average 6-8.
Cuys can have 3-4 litters per year, for a total of 9-12 pups a year. Rabbits can have 4-5 litters, with a total of 24-40 kits a year.
Cuys require .75 sf per adult. Rabbits require 2.6 sf per adult.
In 8 square feet, you could keep 3 rabbits (1 buck, 2 does). In that same space, you could keep 10 cuy (9 sows, 1 boar) .
From the space example, 2 doe rabbits can produce max 80 kits a year. Kits are butchered at 4.5 lbs, yielding about 2 lbs of meat. So, those 2 does could produce 160 lbs of meat in 8 sf.
In the same space, the cuy could produce max 110 pups a year, and average about 1.5-2 lbs at butcher, yielding about 1lb of meat. So, they could produce 110 lbs of meat in the same space.
Cuys can be free ranged, as long as there is protection from predators. They will come back to a home base with shelter, food and water.
Rabbits require 4 ft tall fencing and some fencing underground (or a proper floor). They dig, and you have to take that into account.
Cuys survive on lower quality feed, and fresh greens+grass can be their total diet. Rabbits require higher quality feed, usually good quality hay with some grain.
They both have reasonable FCR at about 4:1.
Rabbits are more efficient in terms of production and space. Cuys do better on homemade diets.
If you have to purchase feed, go with rabbits. If you have lots of local feed resources (grass lawn), go with Cuy.
I have not looked into the Super Cuy breed which has been developed in Peru. They achieve 4 lbs at 4 months old, so have more meat per carcass. They also require more space, so I don't know if they would tip the scales to surpass rabbits.
The best deal would be to have both!