Preview Dialing will allow you to review all information on a given contact before dialing.  Contact info, custom fields, and contact notes will all display, and the agent clicks to dial once they have reviewed all relevant information.  The next contact is pulled up automatically after dispositioning.  See our full article on Preview Dialing here.    

Auto/Power Dialing automatically dials each contact as soon as the previous one is dispositioned.  The same information is displayed for each contact (contact info, custom fields, and contact notes), but as soon as Sales Sling pulls up the next contact, the agent will hear a dial tone.  See our full article on Auto Dialing here.   

Predictive Dialing will call multiple numbers at once and automatically listen for an answer.  When an answer is detected, Sales Sling will push that call to an available agent.  There is no dial tone, the customer is on the phone as soon as the agent gets pushed the call.  Dispositioning works just like Auto/Power Dialing.  See our full article on Predictive Dialing here.