No V-Station is a commercial plugin by Novation but it does give you a very solid foundation on doing subtractive synthesis, plus it sound really good. It's not all that expensive, and interfaces fantastically with the Novation SL Remote controllers. Worth the $s

z3ta comes with a really compreshensive manual and is a really flexible plugin. Next to NI Massive it's my favorite virtual instrument.

All 3 are worth having, but V-Station should be your first port of call in my opinion.