Apistogramma Cockatuoides are probably the most common ones sold, and also one of the easiest to breed. Are you planning on selling privately or to your lfs? If its to the lfs you'll wanna make sure they would buy them from you first, because most already have their own breeders and dealers so they may not take them.
Most Apistos need 'soft water' to breed IMO.
I cut my source water with RO until I get a TDS of 75 or less .. My source water is 350 from tap and too hard for my apisto or rams to properly breed in.
The apistos will prefer a cave. I use terra cotta flower pots on their side so the fish can choose top or sides.. Some prefer the pot be placed upside down and have a small hole in it that the female fits through ,but not the male.
Others will do fine in one of the caves many LFS sell..