Apistos are the best !! But thats because I am biased
. Here are some comments based on my experience.
1. Eco complete is great. I have it on all my tanks. I am not sure it brings out the best colors, but the fish like it.
2. The choice of species will depend on whether you want to breed them or not. Apistos come from soft acidic waters in SA, and some species will require really soft acidic water to breed (pH under 6, TDS < 70). Having said that, A.cacatuoides, A Borelli, A. Trifasciata are probably the easiest to breed in harder and more alkaline water. Your water parameters will dictate what species you can breed. Keeping most other apistos in pH > 7.0 is fine, you just wont get any fry
3. Choice of species also depends on whether the apisto you keep are harem breeders or pair breeders. A.nijsseni for example may kill any excess females. Might be good to do your research on the breeding nature (polygamous or monogamous) before you pick your species.
3. Barlowi is a great apisto too. Getting them might be tough, I usually get mine from fellow hobbyists at forum.apistogramma.com
For getting more information from 'the real apisto freaks', go over to forum.apistogramma.com