Acme 1235. I believe OJ has a comparable one as well but I don't remember the model. Call OJ and Acme and they will tell you the right model for your application.
I have the monsoon 340 with the Acme 1235 and it has made a world of difference from the stock prop.
taek it to a prop repair place, haev them pitch your stok prop down about 2 degrees, it will be almsot as good as the ACME. Myself and friends have been doing this for years. Cost $100
Diggs most people go with the Acme 537 on the HH, that's the 13.5X16. It comes with the Acme 381 I believe the model number is with demensions of 13.5x17.5.