Tough to pick a single one...I'm loving all of Rocky Davies' designs right now, and my favorite would have to be the Dr. Doom "Deal With It" shirt. Abusive comment hidden. (Show it anyway.)
It's impossible to pick even my top five favorites, and I already own so many that I love, but I just came across "Avengers of SHIELD" by Alecxps and am really digging it right now! Abusive comment hidden. (Show it anyway.)