The Hulk is the strongest there is. Everyone knows it, and he’s not shy about saying it. But answering the question of which Hulk is the strongest is decidedly more difficult.
Though Moon Knight is the superhero most commonly associated with dissociative identity disorder, Bruce Banner is also afflicted. He’s been developing alternate personality states, or “alters,” from a very young age, and following his exposure to gamma radiation, those personas have manifested in the real world in the form of various Hulks. Each alter, though they share the same mind, is a distinct individual with its own emotions, desires, and memories.
Banner’s DID is somewhat unique in that appearances by his alters are usually triggered by a specific emotion - and in that they usually involve a monstrous physical transformation.
That’s why the Hulk is sometimes a different color - each Hulk persona has its own unique look to go along with its own unique personality and power set. Overall, the Hulk may be immortal, but his individual personalities come and go, save for the classics, which never seem to go out of style.