I picked Grandmaster for 3 reasons:
1. I loved Robin as a character, and the way I customized my character in Fates with the Grandmaster class resembles my Awakening Avatar.
2.I like the Grandmaster Class as a whole, and helps my Avatar's poor magic growths quite a bit.
3. I loved black trench-coats since I was a kid, so it was a no-brainer. :3