I prefer the black and rust, because the markings are more defined, but I love them all! I have been sharing my life with doberman's since 1984 when I rescued my first black and rust at age of 7 months. My next was a red, then another black and now another black, plus a dobe/greyhound/shepherd mix who is kinda unique in appearance.
I am going to say Black and Rust is my favorite. But I do love all the doberman colors. I have 3 black and rust and one blue and rust.. I would love to get a fawn and a red also but need a bigger house and land first..