Stretch Velvet: has advantages over other velvets.
In hooking the stretch allows for various loop height and width to give interesting contrast to wool. Because of its weight, the loops drape nicely and do not get buried into the backing or adjoining wool. Most importantly, it does not fray or shred as does silk velvet.
In braiding the weight of the velvet provides a plump braid whether stuffed or braided plain.
In applique the velvet can be fused or used as is and since it doesn't fray or shred, it cuts cleanly for a perfect edge.
Taffeta: has a shiny texture, a nice contrast to both wool and the softness of velvet. It has ridges which adds interest and texture when hooked, braided or sewn. It gives a knobby texture when hooked.
Many of the taffetas and velvets come from the same dyepots so are complimentary.