I've been a programming IVR systems since 1994.  I'm experienced with VUI design, grammar building, speech tuning and more.  Here's my opinion on some of the platforms for which I've done IVR programming.

• Avaya has a variety of solutions. I've recently been using the Avaya Aura Experience Portal (AEP) and Orchestration Designer (AOD) for a number of projects.  AEP and AOD are well integrated, providing a rounded solution for your IVR apps.
• Nuance has a comprehensive speech recognition platform.  I really like the reporting tools. Also, check out their OSDM framework, where you can essentially set paramaters and call their VXML subdialogs (there's even a generic one - not just their canned dialogs), and leverage all of their reporting infrastructure.
• Genesys bought the VoiceGenie platform.  I haven't had a chance to use the GVP platform, but I hear it's very similar to the VoiceGenie one.  I was impressed at how well designed this platform is for large-scale implementations.
• BeVocal is great, and provides plenty of logs, documentation, etc.  I particularly like their Vocal Player section, where you can download a packaged file containing the utts, prompts, tts and logs for any call.  The log looks VERY similar to the original Nuance Voice Web Browser logs.
• Visibridge is a simple, stable and lightweight VoiceXML browser that uses SAPI and TAPI.  You can develop and test applications on your laptop, and deploy them on systems that are using VOIP, T1s, analog lines, etc.  The time-trial download is free and you can always grab a new copy when your trial runs out!
• Envox, now owned by Syntellect, has a great VoiceXML browser that's tightly integrated to their existing platform.  I've used their system on a number of projects, and their extensions into their existing platform provides fantastic flexibility for IVRs. Like my Avaya comments, though, their VXML studio tries too much to mask VXML development with their traditional development IDE style.
• Microsoft Speech Server was a fine platform. I started off with Speech Server 2004. Another forcing of an IDE on top of an IVR platform; it was painful! Speech Server 2007 was a complete overhaul, and much better. It eventually became Lync, and then part of Skype for Business.
• Voxeo Prophecy is another impressive platform. It's affordable, the reporting and logging tools are comprehensive, and their support is great.  They were recently purchased by Aspect, and their rapid app dev platform, recently renamed CXP, will be a key feature in Aspect's product line.
• SAP BCM's IVR has limited VXML support in their IVR.  It's more of a traditional switch IVR function than a fully-featured IVR server.  With that said, it does integrate really well with their other SAP technologies.  Another big difference - the scripting language is Python instead of JavaScript.