i'd say guinea pigs and quails are two others that are very good small space users... pigeons too, pigeons are a very common thing i see around here in #madeira in the more spread out, semirural areas

pigeons are actually better for the quality of the food, much better ratio of fat, you can literally be starving of fats if you just eat rabbit meat

but especially if you can place them in a space where you have something else growing, with protection against them nibbling at it, and throw all kinds of garden waste in there and they'll much most green stuff

rabbits are almost ruminants, they eat some of their own poop again so they get more nutrition out of it... and probably there is more fatty varieties of rabbits than others 

 Yes, fat is important! I would think of rabbits as a (very easy) source of protein and manure and plan to get your fat elsewhere.

I don't know anything about pigeons but it's good to hear that they're still common in some areas.