Ive used both before, I've sampled the top dialing softwares available, and I have to say, insidesales has a great system, although I heard lately it may be buggey, it has piecemeal operations that you can buy (like AMR).
Mojo Sales Solutions, is the one I prefer, you can record calls, have different seats, detailed easy to understand reports. They have the ability to have different calling lists, and to have different call numbers to call from (if you have different offices or companies). There is a whole host of options to choose from.
Green mamba is basic, and as long as you have a good connection to your internet, it will dial one number at a time, going down the list with different disposition buttons (outcome of the call).
For all products, they offer custom voicemail recordings that can be left with a click of the button, which can guarantee saturation if your niched in a local market telemarketing.
The difference between dialers is this. An autodialer calls one number AFTER another. A predictive dialer has MULTIPLE phone lines dialing at the same time, which by their logic increases the chance that you will talk to someone cutting down on dialing time, voicemails, disconnected numbers, busy etc.
I think since I have been a telemarketer, a cold caller for other businesses and my own, I will put together a cold calling product so that people can call locally for their SEO services. I have been getting emails to do just that.