this is so subjective. depends on what you like, how old you are, how much money you have, what you eat, whether you have a car, and your luxury quotient.
Parque Rivadavia is a kind of old fashioned upper middle class place, very nice. Villa Crespo is non-tourist urban area, somewhat hipper and younger and more mixed. Chacarita is also an area I would consider, like Villa Crespo more new restaurants, music and art galleries seem to be opening there, but its still far from the bridge and tunnel crowd bars and night life of Palermo.