It really comes down to personal choice. But I see a lot of people buying Cichla by the "flavor" of the month, week or year. I've been lucky enough to have own Peruvian monos, Guyana and Guiana Ocells, broko ocell's, wild kelberi's, bahia's, azuls, tems, floridian ocells, rio meta orino's and so on. But I would take a good looking mono over any Intrem's or Xingu's any day......(I'm lying) just for the fact that I have never owned a interm or a Xingu before. But I would pay good money for a good looking mono.
As for the most expensive cichla now, in the US, I would say a grown Rio Nigro Orino would cost more then a baby Xingu or a baby interm. Those cichla are on top of MY must get cichla. 24k Ceara's to.
As for having the nicest patterns/markings, I would have to say Wild kelberi's. You have the mono colorings of the yellows, greens and reds, but the gold spangles on the tail, anal fin and dorsal fin. So, kelberi's get my vote for nicest patterns and markings.