I'm an RTAS man but back in the day when I was using free VST's on Kristal I really liked Ambience.
+1 for Ambience
It is not the best and not the smoothest reverb but i like how it sounds.
IK's Classik Studio Reverb has become my go-to, aside from a few particular convolution impulses.
For algorithmic reverb, I can't find anything that can replace the Arts Acoustic reverb..