Hard vs soft dialers
I believe you are referring to the difference between predictive and preview dialers? Predictive meaning you give the computer a list of names, and when it reaches a customer it then tries to find an available agent (it tries to predict when an agent will be ready for another call and have a call ready at the same time). And Preview meaning that the agent is given the record, allowed to read it and then tell it to dial that person (the agent is already on the line if the caller is available). Or there is a third option where the dialer waits for an agent to be available and begins calling until it finds a record for them, but I am not sure what the official terminology is for it.
In my humble opinion, you need to decide what your priority is: Quantity or Quality.
If you just want to get through the list and talk to as many people as possible with the fewest agents, then Predictive is the way to go. Most Sales applications use this. It is rather irritating to customers, because the dialer will often reach a person and not have an agent available. At that point (here in FL at least) the dialer has to hang up (called Dropping on my dialer), leaving an angry person holding a dead phone. Or if there is an agent available there is generally a couple of seconds delay before the agent is actually on the line (the predictive dialer tries to determine if the customer is actually an answering machine). Many people here in the USA (myself included) hang up when they hear the delay.
The Preview dialer is slower, because your agents will have to sit through the ringing, busy tones etc... But you don't hang up on people and there is no delay so people are less likely the hang up. But this does require more agents and has fewer contacts per hour. (not sure of the exact ratios)
FYI: we have both here are my company and generally use the Predictive for Sales and survey applications, and Preview for Customer Service related applications.
Best of Luck,