I use 200 lb green Tuf line XP. I bought the 150 yard spool and split it between two downriggers - I think it was cheaper than going with the Scoty line. Diameter is 0.028 inches, I think the Scotty Dyneema line may be a hair thicker. I use the new Scotty stops designed for braided line and I find they still move, however, maybe only a few inches each trip. Godd idea to glue them in.
If you catch bottom and need to quickly break off it's a heck of a lot easier to cut with a knife then look for your wire cutters for the cable.