I've never participated in this before, so please be patient with me!
My favorite robot masters are Hardman and Cutman. However, I love all of the robots from Mega man 3, and anything involving them will be appreciated too! Other favorites are Bombman, Fireman, Roll, Quint, Woodman, Splashwoman, Honey/Vesperwoman, Toadman, Sheepman, and Bounceman.
I also love Megaman Fully Charged, and my favorites from the show are Cutman, Fireman, Drillman, and Waveman. Mini is also appreciated.
I am totally fine with receiving something with just one robot master in it; you don't need to include a bunch of different robots unless you have a collage idea