I'm not a fan of Sampletank. Granted, I didn't give it much of a chance and only used their free version. I don't even know if it was version 1, or 2. I just know the sounds were thin. Unless I was doing something wrong, everything sounded over-processed and somewhat distorted, or at least harsh-sounding.
On the other hand, NI makes some really good stuff. Even if you were comparing it to the Kontakt sampler, that's a really good and expandable sampler and it includes a sound library. As far as the Komplete 8 bundle, that alone gives you a ton of sounds and endless possibilities if you use Reaktor to make your own synths or use the included ones. It's really not a fair comparison.