I like anything with a unique shape and/or stunning colors and patterns. I like the personality of bettas and the different wild species. Celestial pearl danios and Pseudomugils and another favorite of mine. More;
Parachromis
Gar
Crenicichla
Bagarius
Geos
Apistos
Rams
basically, anything unusual.
Its possible to breed killis!? I thought they all must have been wc or must be mass produced in asia. I didn't think they could be breed on a hobbyist scale. I had a school of 10 when i was like 6. But then i installed a hob filter because the underground one was a p.o.s. Sad to say but they swam up the intake and met the propeller...