I would build something on the lines of a speed entropy rainbow: Puppychows or Butterfly Angel. Of course it depends on how many Shards of Gratitude you have? Also take a look at CC? Why Bother, then decide which route you'd like to take... you will then get help in deciding which cards to upgrade first!!!
Alternatively... ScaredGirl's almost unupped FG killer was a good starter, but I dunno if it's still working as well with the newer Gods.
PS. before I forget, it's handy to keep a few electrums back, as it can be costly losing 10 FG battles in a row - this happens even with fully upgraded decks!!