That's simply because I like Sonic characters! They each could have unique playstyles, Shadow's being the most unique. He could use energy blasts, teleportation, spear projectiles, a chargeable time freeze, and yes... even guns.
I would love to see Dark Samus and K. Rool though. I really wanted K. Rool in Smash 4. I don't even like Donkey Kong, but K. Rool has such a fascinating design. It's so revolting and unique. As a kid he really frightened me, but I realize now that that is the very thing that gives him strength.