I think for the long road, Kontakt is nearly a "must have" to get the highest quality and coolest libraries. It comes with an almost bewildering amount of content right out of the box, and the libraries you can add to it are the best around. Warning,,, buying cool sound sets is addictive, though,,,, lol
If you went with Komplete, you also get Guitar Rig, which you may find useful. You also get some really top quality synths and a ton of drum stuff and sample crunching stuff. Overall, it's a power package.
I'm new to it and I've spent a ton of money on stuff I probably won't use much, now that I have Kontakt.
It's not cheap, but it's sweet. You can get whatever you want now,,, but I can almost guarantee that you will eventually want to have Kontakt.
ETA,,, I just got Komplete and I'm blown away,,,