Honestly, I've heard of a lot of transguys saying that a buzz (Even a longer one) usually accentuates the feminine features in your face, that and it accentuates the shape of your head, which I heard is bad for passing. I've read a lot about haircuts on FtMs and a lot of people suggest getting it short on the sides and just a little longer on the top - think of a typical business man's haircut. I hear that the 'Traditional man's cut," and "Traditional boy's cut," is most popular among most FtMs.
And then...there's me...I'm not like most FtMs xD My cut is EXTREMELY unconventional. The sides and back were all cut to a 3 and the top is approximately seven to nine inches long in the front. I have it swept to one side and then it's angled to be shorter in the back, much like an a-line. Mind you, I have huge hips and a huge ass, and I can't hope to pass, even now that I'm on T, but the cut suits me well - for now anyway.
Good luck!