Brave Blade, or Chicken Knife?

[BFM]

I'm at the point in the game where I can decide on whether or not I want to get the Brave Blade or the Chicken Knife, which do you think is better and which would you reccomend that I get? Also does anyone have an idea as to how often the Chicken Knife forces you to flee battle? (Preferably some kind of percentage or ratio.)