Since there are more than 600 species (as of 1998) of new world cichlids, this is a very difficult question. And in 50+ years of cichlid keeping, I've only kept about 75 new world types.
Maybe if it was narrowed down to countries, or geographical areas.
I might say of the Caribbean cichlids haitiensus was my favorite so far.
Or if you were to say, the cool water cichlids of S America, I might say the genus Gymnogeophagus.
Or even rheophillic cichlids of Central America I'd be hard pressed to pick lentiginnosum
or what about the cichlids from west of the Andes, there is just too long a list