Recently I used Wizooverb's W2 (2 different IR's) on Sarasate's Zapateado and Massenet's Meditation. I used GigaPulse on Prokofiev's 2nd Violin Concerto. I find that W2 can be sweeter and softer on strings than GigaPulse. However, GigaPulse often does a better job (my opinion) on creating depth, and I love that way Gigapulse's large hall IR makes french horns sound.
Hopefully MIR will provide the best of both worlds. I would also love it if AudioEase decided to port Altiverb over to the PC as I'm consistently impressed by the Altiverb sound.
Best,
Jay