Sorry, missed the wireless part... Have been around a couple, none that i liked. Dont let the wires scare ya, install really is not bad. Its also way more versitile. We maximized our lots to allow as much free roam as we wanted, and have wire run in front of garages, so they can come in the garage, and not go out the open garage doors etc.
No idea how your lot/land is like though, and how youre wanting to contain them.
Buy one setup, and work with each dog individually, to see how they respond. It should be easier to get them used to the collar without 4 others theyre paying attn to. As well as, saving the cost of 4 extra collars until you know it works for your dogs.