I loved going into anti-form, even though it has often led me to dying when dealing with bosses and I change. Not being able to cure sucked, but great considering that this is, basically, his Heartless form and thus is accurate.
But, I really liked Master. For some reason, even though the costume was yellow, it was my favorite to play with and as. I liked Valor as well, and I used it the most, but Master was the best.