Aeneus are by far the easiest to breed. But they have to be full grown, fully mature. If they are not, all the cool water changes in the world won't do a thing. There's no mistaking a female cory close to spawning. They get so round around the middle that you could easily think they have dropsy. At this point, even without a water change with cooler water...they will spawn. Most cories like to spawn in the early morning hours. You may notice a flurry of spastic, crazy activity while glancing at the tank. The males go a little nutzo when they are after the spawning females. I feed lots of frozen blood worms to all the cories I've bred. Some cories take longer to mature than others. Take sterbai for instance...they will not be spawning until after 2 years of age. Keep to the bigger cories until you get some experience under your belt. Then you may want to tackle a cory species that's a bit more difficult. I always heard sterbai were difficult to breed but found them very, very easy.
As far as the black cories.....They are not often available. I have a group of 12 that are well over a year old but showing no signs of nearing spawning shape. So it looks like these guys need lots of owner patience too.