It depends on the size and the weight of the napkin for me. The napkins I use are pretty sturdy and 22x22. So I usually just use wash away on the bottom and on the top. The topper helps to keep the stitches from sinking into the fabric. If the design is dense or even dense in places, I use a med weight tear away on the bottom and wash away on the top. I avoid very dense design because they leave the area feeling too stiff for my taste. I don't like the feel of the dense design on my hands when using the napkin. I also like to use a napkin that is a blend of 50/50 cotton/poly. Most women don't like to iron any more, so the poly helps with that. The cotton makes the napkin more absorbant than just a 100% poly napkin...but the poly napkins are less expensive.
Either wash away or tear away, depending upon the fabric and design. For a heavy dinner napkin with fairly dense monogram design, I would use a tear away stabilizer, if the napkin is light weight and the design is more similar to red work, I would use WSS. I have not had good luck with sticky back stabilizer: gummy needles and left over residue that is difficult to remove.
I use a wash away and match my bobbin thread to the top threads.
I love using sticky back Vilene. You only hoop the stabilizer. Sonia Showalter has some lovely tutorials demonstrating her designs.
I would say wash away ? but let's see what more experienced Cuties say.