My experience is that the deck authors tend to over-state the ability of their decks. For this reason, I would suggest to use decks that are aimed for farming higher levels, e.g. gold or platinum, so you can try "Gold League killer" or Splat and will get a good win-rate in silver.
If you try decks that are listed as good silver-killers you will get over 50% wins, but not high enough consistency for special spins.
However, if your aim is to get shards quick, then use a fast speedbow (eg.. Arena farming 101) in bronze, that gets the job done the fastest.