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The older/earlier/legacy AutoQoS was to support VoIP. The current(?) SRND4 AutoQoS supports Cisco's 12 class QoS model, which also includes VoIP. (BTW, the AutoQoS version doesn't depend so much on the vintage of the device as it does on the vintage of the IOS version.)
I'm unsure how the two will intermix. I suspect both use/expect similar tags for VoIP traffic, but buffer management settings might differ, which could lead to very different VoIP performance, based on your actual traffic mix.
Personally, I've found it better to define your own QoS model, and its supporting device configurations, to meet your QoS goals rather than use the AutoQoS models. (This also avoids unexpected "surprises" if you upgrade your IOS version.)
I can appreciate the thought using AutoQoS will make a QoS deployment easier, but the time you might need to spend "debugging" what AutoQoS does might be used for building the QoS you need. (Of course, AutoQoS might work just fine for you too.)
