IMO, other than age of software and support disposition there isn't anything major that is different between 5, 7, or 8. Unity 5x and 7x are, for the most part, the same thing except that 5x has reached EoS/EoL and is in that cycle now. Unity 8x is in maintenance mode. This means that no new features are being developed and it might well be the last version...however, it'll likely be around for a while due to install base. Cisco is pushing Unity Connection with Single Inbox as a better, more flexible product. So, here's the bottom line:
If you are set on or have to stay on Unity for some reason and your hardware supports it, go to 8x. The process will be the same either way. If your hardware isn't supported for 8x then just go to 7x...this is really a "6 in one hand, half dozen in the other" scenario as far as I'm concerned.
If you want to stay with Cisco for messaging but would like to position yourself for the future, you should consider migrating from Unity to Unity Connection. The COBRAS tools make this easy for you and if you have the proper support in place then you can generally migrate from Unity to Unity Connection at no or very low cost (generally depends on hardware).
Hailey
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