She-Hulk: Attorney At Law brings back Abomination after a lengthy absence from the MCU. Abomination numbers among the most powerful Hulk villains in Marvel Comics, with strength nearly equal to the Hulk's. While he didn't get a rematch with Hulk (yet), many other great villains likely face off against the green Avenger in upcoming movies and shows.
The Leader returns in Captain America: New World Order, bringing back another powerful Hulk villain who so far hasn't gotten his due in live-action. Many other great Hulk foes likely appear in the near future, including some like Wolverine that Marvel fans have been looking forward to for years.
Wolverine
Wolverine made his first appearance in Marvel Comics in The Incredible Hulk #181, starting out as a great Hulk villain before joining the X-Men. Though Wolverine's powers evolved after his debut, he still brought superhuman strength, speed, and agility to the fight, proving a difficult opponent for Hulk.
Wolverine, easily among the most powerful X-Men in the comics, also wielded his trademark adamantium claws. This made him especially dangerous, even for the Hulk and his durable skin.
Zzzax
Zzzax exists as pure electricity, giving him vast electrical powers. He generates and absorbs electrical energy as he did in his debut in The Incredible Hulk #166 from 1973. He also controls machines to some extent by manipulating their electrical components, allowing him to access information or assemble an army of robots and drones.
His powers allow him to electrocute and incinerate his opponents, but this doesn't work on the Hulk, Still, he's proved a difficult villain for the Hulk to overcome time and again. She-Hulk also fights Zzzax in her comics, opening the door to his appearing in the MCU show in some form.
Xemnu
Xemnu originally went by the title The Hulk, first appearing in Journey into Mystery #62 years before the Hulk appeared. Not only does he possess considerable superhuman strength, agility, and endurance, but he counts among the most powerful psionic characters in the Marvel Universe. Xemnu generates hypnotic rays that can control an individual or even large crowds.
He uses this ability to effectively survive any injury. Xemnu reforms his consciousness from an atomic level and can take over another person's body, physically altering them to transform into his giant, white-furred form.
Red Hulk
Red Hulk counts among the strongest Hulk versions in Marvel Comics. His strength and invulnerability rival the Hulk's in scale and he also possesses other abilities Hulk doesn't. Red Hulk absorbs and emits gamma radiation, which can kill people in his immediate vicinity. He also breathes fire and even catches fire when he becomes overheated with anger.
Red Hulk also absorbs cosmic energy in all its later forms. This makes him potentially unlimited in power, as he showed when he absorbed the Power Cosmic, briefly becoming a powerful cosmic being.
Hercules
Comic book fans know Hercules numbers among the strongest characters in the Marvel Universe. The Olympian demigod possesses superhuman strength and stamina equal to the Hulk's, as he proved in their initial battle in Tales To Astonish #79. The two battled to a stalemate, with neither able to outright defeat the other.
Hercules also wields the Golden Mace, a powerful weapon made from the god-like mental adamantine that rivals Mjölnir in terms of power and durability. The mace also channels powerful energies on occasion.
Maestro
Maestro possesses all the superhuman strength, speed, and stamina of the regular Hulk, including his ability to leap incredible distances. No limits exist on his strength as his capacity for power relates directly to how angry he gets. Maestro gets very angry, though his greatest ability lies in his cold, calculating intellect.
Maestro, introduced in Future Imperfect, among the best Hulk comic book storylines ever, combines Hulk's strength with Banner's genius. He also abandons all morals and ethics, ruling a dystopian future with savage brutality.
Abomination
Abomination possesses superhuman strength that actually exceeds the Hulk in some ways. He benches over 100 tons, over what the Hulk initially could do. The Hulk's strength amplifies with his anger, however, unlike Emil Blonsky's. His strength remains static, though Blonksy's own baseline for power has increased over the years.
Abomination shares a healing factor with the Hulk, making him essentially invulnerable. He also enters suspended animation in some extreme cases, going into unconscious stasis to heal or hibernate for indefinite periods of time.
The Leader
The Leader lacks the Hulk's impressive strength and speed, but he more than makes up for it in his psionic capability. The Leader combines his natural genius with gamma-augmented brain power, making him extremely intelligent. This also makes him incredibly inventive, allowing him to create androids called the Humanoids who have overwhelmed the Hulk at times in the comics.
The Leader possesses vast telepathic and telekinetic powers that don't always work against the Hulk but give him a different instrument to use instead of raw, brute force.
The Illuminati
Comic book fans know The Illuminati comprises the greatest minds and powers in the Marvel Universe, including Professor X, Doctor Strange, Mr. Fantastic, Black Bolt, Namor, and Iron Man. They also possess a cutthroat approach to dealing with major threats, which they displayed when they exiled Hulk to Sakaar in the Planet Hulk storyline.
The Illuminati set off a tragic series of events that eventually led to Hulk returning to Earth with a vengeance in World War Hulk, a major comic book storyline that the MCU may be setting up with his return to Sakaar in She-Hulk: Attorney At Law.
Himself
Hulk's greatest villain in Marvel Comics is arguably himself. From his first appearance in The Incredible Hulk #1 in 1962, Bruce Banner fought his anger and rage, often succumbing to it. The Hulk generated massive destruction Banner couldn't control and even when has achieved control, he still wields unimaginable capacity for violence.
A 'smart Hulk' like Maestro or even the Hulk that destroyed New York City in World War Hulk proves more dangerous than the original brute, and the same may hold true in the MCU.