Between those two I'd lean towards the BK. I mean really you're gonna spend over $600 bucks on a frame and not even be told what its made out of?? If you're for being a guinea pig and going out and trying it then go for it.... But with the BareKnuckle you know what you're getting, a relatively stiff, tight geo, overall great riding (IMO) bike
I suppose it also depends on what you wanna do with it. The stainless lugs on the Leader frame will tend to have a bike that is a little bit more classic or retro looking and you can spec a build that will leave a similar feel.
On the other hand the BK with its slightly larger tubes and straight blade fork you can play around with the look a little bit more.
FWIW, I have a BrassKnuckle that I ride day to day and a BareKnuckle that is going to be built up as time goes by. So I guess I already made my decision....best of luck and have fun!