I use the water soluable stabiliser top and bottom so that there is no visible stabiliser left after embroidery. Works for me every time.

I use trick film a twin to clear n melt. It shows no stabilizer on back.

A water soluble on top and bottom should work well.

Generally I use a tear-away on the back, and a thin solvy on the top.

The other "secret" is to use organza. This works especially well if you have more detail in the design -- or at least "detailed edges" to the design. Layer 1)Towel 2)Solvy 3)Organza -- that way when you trim the organza away, you're not fighting your scissors with the towel/terry loops.

The organza keeps all the fine detail of your design around the edges from getting buried. When you're done stitching the design, trim the organza away about 1/8 to 1/4" from the edge of the design. Organza comes in colors, but it basically "disappears" in the towel, so any color even close works well.

It makes a huge difference in your finished design. Even fairly small lettering comes out fine on towels!