Native Instruments Komplete 9 and Komplete 9 Ultimate

Native Instruments, Kontakt 5 Player; A sampler you can use as a standalone or as a VSTI with a Digital Audio Workstation. It is included with Komplete 9 and Komplete 9 Ultimate.

Pros:  

You can use Kontakt 5 with sounds from the Native Instruments library, and from other music libraries that support Kontakt 5 format.

Example would of this would be Project SAM; it has products are used for Kontakt 5, like Symphobia and True Strike.

Also the sound Quality from using Kontakt 5 is incredible, as the Virtual instruments used have the same distinct quality sound as the original Instruments.

Cons:

Even though Kontakt 5 is a free Player, the actual products are what you are paying for, most of the outside Native Instruments libraries cost as much as $1000, an example of this would be Lumina, a Project SAM orchestral library that was released for Kontakt 5 is $1099.

You will also need a decent size hard drive for your PC as most libraries can range from 20gb to even 200gb of sounds.  You computer will also have to be fast as well and the loading times can be an issue if you have a slow PC.