I use mostly internal stuff for Sound Design + ALL FabFilter plugins (Rocking GUI and sound possibilities)
For Music? Softube Tube-Tech + Steinberg RND Portico (Excellent vintage feel) and again surgical excellence via FabFilter
I sold all other plugins (Slate Digital, Softube etc.)
IMO, one hidden gem in the stock plug-ins is the Brickwall Limiter. This is excellent for transparently limiting only the extreme peaks in the audio without effecting the rest of the signal at all. Surprisingly few limiters can do this since most have been designed to maximise the signal.
Post Filter is really good too.
Some people don’t view this as a plug-in but the tuning function built into Nuendo is a god. I had to actually read the manual to learn its higher functions but once I did I realized how powerful it was. In February I had to tune lead vocals for 20 songs for a kids show where the lead couldn’t really sing but after going through each song note for note reading the score you could barely tell. All done in real-time too no rendering required.