Invision is the application name for Intervoice, who is a major global player in IVR systems. The advantage with Intervoice is that they work with any PBX/ACD manufacturer, and any back end systems. At my old company, we had Intervoice IVRs tied to Avaya and to I3. If you are a pure Avaya shop, you may benefit from Aspect - one number to call for support, cleaner integration. If you have any other systems, or may acquire and companies with legacy systems, you may benefit from Intervoice. But from what they do, and what the customer experiences, they are both pretty similar.