fwiw, Kontakt's probably my favorite plug. Like you, I tend to like organic and realistic sounds.
I think NI has a promotion going right now through end of month where if you already have Komplete Select (which comes with their keyboards I think - then you can upgrade to Komplete Standard (which includes Kontakt) for $199. I \_think\_ that's right, but check me on that. If you don't already have alot of sound libraries Komplete Standard has alot of instruments and sounds that would be useful including pianos, organs, drums, guitars - along with their synth stuff.
$1I have Kontakt so I can upgrade to Komplete Standard for $199, and I'm considering it - but I' almost sure the same discount applies to customers who already have Komplete Select - which I think comes with most of their keyboards.
My conundrum is I already have so many other 3rd party instruments (mostly for Kontakt) that most of my musical needs are already filled - but if I didn't already have those sounds Komplete Standard which includes Kontakt would be a no brainer for me. There are so many inexpensive (and many free) sample libraries available for Kontakt that it opens up so many options.
Good luck.