I own both. You get the same excellent engine with either product.
I have to admit I was very surprised to discover how unplayable the Italian Grand was for me, especially given how nice the demos sound. I am very particular about the softer dynamics, and I found Italian didn't suite my style at all. I stopped playing it after 5 minutes and doubt I'll use it again.
If you like the sound of Yamaha, Ivory II Grand Pianos is probably as good as it gets today. The Yamaha sample set is very clean and plays well. I'm more of a Steinway guy, and I'm disappointed with Ivory here. There is a sort of overlaid crackling artifact on the lower velocity samples that I find very unpalatable. This is really very frustrating as it's otherwise nearly perfect. It should be said that when I pointed it out in the "First Impressions" thread, it didn't seem to bother other people as much as me. You can decide for yourself
Nowadays I favor the Galaxy Vintage D, but I pine for Synthogy's excellent and stable engine. (Well, the VST is stable. Cantabile is not.)