For myself, I can't say any one type is my favorite, but in genreal I like colorful fish, and smarter fish. Those fish who can defend their nest, protect their eggs and fry are the smartest ones in my opinion. Fish like Gourami, Betta, Cichlids, Angelfish (still a type of cichlids), all put some level of responsibility into protecting their next generation. So they are all on my favorite list.
I still remember how amazed and amused I was when my first Dwarf Gourami was building a bubble nest with my plants and his bubbles. It was awesome to look at him defending his nest. I tried to pull his nest away from the filter outflow, and he attacked my finger! He hit really hard for his size, too. The level of care he put into picking up each individual egg and fry and then put them back into the bubbles was a cool scene, and would not be expected by most people who know little about fish.
My German Blue Ram would also defend their nest. Even the two of them are both female = no fry.
