Because each Type of PFD has different advantages and disadvantages, the best kind of PFD is the one you are most willing to wear.
There is no standard time limit for PFDs. This depends on how often you use them and if they have been properly maintained. If your PFD smells of mildew, appears waterlogged or shrunken, it is time to replace it.
Type V, hybrid flotation is only partially inherently-buoyant, meaning there is a minimum amount of foam flotation material built-in, and is either manually or automatically inflatable via the inflatable bladders inside. Most often, hybrids are used by those wanting a minimum amount of flotation, and wanting the option to have a low profile device by those do not commonly come in contact with the water.
No. All people, swimmers and non-swimmers alike, are naturally buoyant. Type I, II and III PFDs offer between 15.5 and 22 pounds of added buoyancy, while Type Vs add between 7.5 and 22 pounds. Because most adults need between 7 and 12 pounds of extra buoyancy to stay afloat, all USCG-approved PFD Types will work for those who don't know how to swim, except for inflatables.
If you are using a Type III, then yes. If referring to a Type V, no. Type III PFDs are approved for use in conjunction with various water sports, while Type Vs are only USCG-approved for the kind of activity specified on the label. Read the label to verify the PFD is approved for your particular use.
Boating can be unpredictable. It is much safer to stay strapped in during your time spent on the water than risk your personal safety for the sake of comfort. It is recommended that you wear your PFD at all times while underway.
Annually. To ensure buoyancy is intact and wear hasn't eroded the integrity of your PFD, perform checks on all the hardware and flotation at the start of the boating season.
Unfortunately, no. A PFD can help reduce heat loss by making it easier to float, while also forming a barrier between cold water and a wearer's skin, but will not prevent hypothermia. When venturing into cold water, consider wearing a wet or dry suit under your PFD to further protect yourself from extreme conditions.