Okay, you want ways in which Sonic the Hedgehog was different from Super Mario Brother:
Projectiles: Mario could gain powerups to use projectiles, Sonic could not.
Structure: Mario used a x-1 to x-4 structure, with a variation of the same boss. Sonic 1 had a X-1 to X-2 structure, using fundamentally different bosses.
Music: Each level in Sonic had a musical theme associated with the area, in Mario, each stage had a music theme associated with the stage (water music, under ground music, castle music, and overworld music.)
Gameplay: SMB had a simple left to right structure where you had to jump over obstacles to progress. Sonic had a flexible scrolling which could have you going from left to right then down, then left, then right, then up.
Puzzles: SMB had none, save from the last castle in which you had to, by trial and error, figure out where to go. Sonic had switches and various things to use to progress.
Even if you compare SMW to Sonic, SMW coming after Sonic, you have little similitude, and at that point, these elements may have been lifted from Sonic.
However, if you still wanna claim that Sonic is a copy of SMB, then I claim that SMB is a copy of Pitfall.