It seems like your tank is bigger than you thought, FishNMusic. That does change the discussion a little bit. But that still eliminates the Jaguar Cichlid. A mating pair of Jaguars will need more room than that. It can be done simply because cichlids can mate before they're fully mature. This is only short-term confinement though.
You might be able to pull it off with Green Terrors. You certainly can't have a pair of GTs and a community of other fishes in there with them. Just the two would be pushing it.
I believe you can probably house two dempseys in a 36" tank. I kept one in a 48" tank, along with an orange pike and a buttikoferi once. The pike and tilapia were not fully grown, but even so, they were big fish and there was plenty of room. You might be able to pull it off in 36" 30 gal.
Take your tap water into consideration for breeding purposes. That might make the choice for you. Cichlids can live happily in a wide range of ph and hardness, but they may not breed unless those values are close to ideal. If you live where the water is hard and alkaline, go with the Rift Lake cichlids. If you are lucky enough to live where the water has little hardness, then you can go with the south americans. Or you can do what I do and use reverse osmosis to top off the tanks even though I do not breed.