Who is Sonic's worst enemy?

Ah, an intriguing question indeed! So, let me ask you this: who do you think is Sonic the Hedgehog's worst enemy? Is it the nefarious Dr. Eggman, with his endless array of deadly robots and schemes? Or could it be Shadow the Hedgehog, the enigmatic and powerful rival who seems to constantly challenge Sonic's position as the fastest thing alive? Perhaps it's someone else entirely, lurking in the shadows, waiting for the perfect moment to strike. But ultimately, who do you believe is Sonic's greatest foe, and why?