First we have the live prey, where live animals (either bred or bought) for this purpose are give to the ferret. Animals being purchased for breeding or feeding purposes should be done so from reputable sources to ensure the animals are healthy and free from any parasites.
Usually if you purchase any F/T wholeprey from petstores, they should be in good form and health but it doesn’t hurt to check. Live prey is usually done in a bath tub or somewhere closed off like a bathroom or tiled room. Frozen thawed prey is often bought pre-killed / pre-frozen from stores or breeders and is fed thawed out and or as is. It is easy, convenient and readily available to most people. Especially if it is Rats or Mice. Fresh and dispatched prey is something breeders who are experienced in humanely dispatching animals may do. People could simply buy the animals and dispatch them if they wish to do so but they must have the experience. I do this myself as I get the added bonus of the enrichment my ferrets get from how fresh the food is without the added risk unnecessary suffering of it being alive.
F/T is the most simple and easiest choice, many will choose this over the others. Breeders or people who know how to efficiently and humanely euthanize may do fresh and dispatched.
Ferrets may take to fresh food more than they would frozen/thawed food as it is still warm and enticing. This often tricks them into believing it is alive. There is a difference in textures when you compare F/T and F/D wholeprey, although it really isn’t much to be a concern. Some ferrets may have similar reactions with Frozen Thawed, however being an active breeder for wholeprey, I really have seen the difference fresh makes compared to pre-frozen and thawed food. I find my own ferrets are more interested in the food and will eat on the spot more than they would with frozen thawed food. That is just based on my personal experience and it may be a different case for others.