What's missing from your current tools? If you just need sculpting/painting then ZB is the reigning champion. Or do you need a more complete modeling / texturing / rendering package? Then Modo or C4D/BodyPaint might be a better choice... the other factor might be which platform you use. As I've heard ZB3 still has not released a Mac version, and it's due about 2 years ago
I don't like using ZB. Modo was more natural for me. But "to each his own". This is where i advise you to "try the demos"...
jonah