Most Watchmen fans insist to me that Dr. Manhattan can take on literally anyone ever. I have people telling me he ranks above The Living Tribunal. So I have looked up various characters, and have picked the weakest character who i believe could give him a run for his money. I believe that Dr. Manhattan would prolly beat the Silver Surfer 8/10. Their powers are very similar, with Dr. Manhattans advantage of seeing time differently. However, I believe that He would most likely get destroyed by forces like The Beyonder, Galactus, or The Phoenix Force.