A) I don't really care for the TNG Klingon episodes as a rule.
B) These are probably my favorite, but not necessarily because of the Cardassians. The Wounded is a fine episode, but I probably like it more for O'Brien than the actual Cardassians. Chain of Command is a fine serial for all the obvious reasons. Honorable mention to The Chase.
C) Romulan episodes are pretty enjoyable, with The Defector, Data's Day, Face of the Enemy, and Unification being very enjoyable.
D) Can't go wrong with The Best of Both Worlds.
E) Eh, no thanks. Their portrayal was more entertaining in DS9, but I think as far as TNG goes, the best representation of the Ferengi comes in Future Imperfect.