My favourites are ReLab LX-480, Valhalla Vintage and Plate. I use Valhalla Shimmer and Guitar Rig Psychedelic Deleay on some piano solo tracks sometimes, I found the right balance and I really like it.
Many years ago I tried the EMpty 250 and I thought it had a very beautiful, lush and open sound but was very buggy and CPU hungry.

 

Denise audio perfect room 2 is one of my favorites

 

I recently rediscovered the Lexicon PCM bundle, and I’m stunned every time by how well it creates a sense of space.
But I think the most impressive thing is how you can use multiple instances on different sources, really go overboard with it, and the mix still doesn’t get muddy.
Also, the PCM Rooms are fantastic on the drum bus. They add a very live, organic character to electronic drums.