What type of device should protect hose connections such as silcock's and hose bibs?

The best device to protect hose connections such as silcocks and hose bibs is an atmospheric type vacuum breaker. This device is specifically designed to prevent back-siphonage—an occurrence where contaminated water could be drawn back into the drinking water supply.

The atmospheric vacuum breaker operates by using an air inlet valve that opens when there is negative pressure in the system, allowing air to enter and thus breaking the vacuum. This helps ensure that contaminated water doesn't flow back into the potable water supply, making it particularly effective for applications where hoses might be submerged in or used with potentially contaminated water.

In contrast, while other devices like a pressure type vacuum breaker or a double check valve have their own applications and functions in backflow prevention, they are typically used in scenarios that involve higher risk or more complex plumbing systems than those associated with simple hose bibs. A backflow preventer provides a general means of protection against backflow but may not be necessary for every type of hose connection, especially at a residential level. Thus, the atmospheric type vacuum breaker is the ideal choice for the specific context of protecting hose connections.