I'm not really a fan of convolution reverbs because of the lack of possible tweaking. I very much like the Lexicon 960 which I rent when I have a surround mix to do.
I quite like the 960. I have a much harder time getting nice reverbs out of a pcm90 or 91. Even the 300 is tricky sometimes.
The difference between the models is the dsp power, i.e. complexity of the reverbs, and thus the complexity of the algorithms. But I'm not too surprised that you like the results of your lower cost units better than your altiverb. There is something "live" about algorithmic reverbs which I miss with a convo reverb.
That said, for the chamber music I currently mix I very much like the convo reverb I have at hand. It is just there and not noticed as something added to the instruments. This is different than how I mix orchestra: In a orchestral setup reverb is more of an instrument, for example my recent film music is mixed more as a "music for orchestra and reverb".