I have Komplete 8 Ultimate and it's amazing. It's worth having for Reaktor alone - that amazing instrument could keep a person occupied for the rest of their life. The effect chains you can set up with Guitar Rig are incredible. However, I will say this. Sonar seems to have some issue with Guitar Rig hosted effects in which it will occasionally zero out all the controls upon loading the project. I've had to reconfigure huge effects chains a few times because of this, of course I should really be saving them as new presets! But it does happen, and since I used exactly the same plugs in Pro Tools without issue I'm going to presume it's a NI/Sonar clash. I've never managed to get to the bottom of it and nobody was helpful on NI's forums.
But despite this, I still think it's one of the best VST collections anywhere and definitely the best value for money.