Wolverine is the best at what he does, and what he does (aside from drinking tons of beer, wearing out countless tank tops, and repeatedly getting cloned) isn't very nice. From his first appearance in The Incredible Hulk #180, Logan has garnered a reputation as being one of the deadliest heroes in the Marvel canon.
While he's particularly lethal when compared to your average X-Man (or X-Woman) among the Avengers he's on a much more even playing field. It goes without saying that the amount of power he brings to the table pales in comparison to Thor or the Hulk, but the Avengers have had some other members over the years that are surprisingly more dangerous than Wolverine.
10 Hyperion
A former core member of the Squadron Supreme, Hyperion joined the Avengers in Avengers vol. 5 #1. Hyperion is Marvel's version of Superman, at least during times when the Sentry isn't having a mental breakdown.
He has Hulk level strength, super speed, the ability to fly, and is impervious to pretty much anything other than "argonite" (his version of Kryptonite). An Avenger with the abilities of Superman is potentially the most dangerous person on the team, depending on their moral code.
9 Moondragon
Just a reminder: Moondragon is probably the most capable telepath in the Marvel Universe. She's so powerful that she was able to mind control over Thor along with millions of others all at once. Raised on the planet Titan by Mentor, father of Thanos, she was trained by the monks of Shao-Lom.
What's crazy about Moondragon is that she gained her powerful telepathy through years of rigorous training of her latent psionic abilities, which are allegedly present within all humans in the Marvel world. Her mastery of martial arts also makes her an extremely formidable hand-to-hand combatant.
8 Captain Britain
An agent of MI-13 and fabled protector of the UK, Captain Britain's tremendous power stems from the Amulet of Right, a mystic artifact gifted to him by Merlyn himself. The Lion of London joined the Avengers during the Age of Heroes miniseries and even served as part of Steve Rogers' Secret Avengers during the group's first incarnation.
Captain Britain's powers include superhuman strength, endurance, and speed, while his Star-Sceptre, a weapon also gifted to him by Merlyn, gives him the ability to fly at near sonic speed. As his father was a resident of Otherworld, a realm created by the collective unconscious of the British Isle's residents, he has a powerful connection to magic.
7 Hercules
The Prince of Power, Hercules is a legitimate god of Olympus. The list of his feats of strength is as extensive as it is ridiculous. This guy can go toe-to-toe with Thor and the Hulk, and is strong enough that he was able to topple Godzilla when the King of the Monsters battled the Avengers back in the 70s.
In the Marvel Universe, Hercules is the Greek god of Strength which makes him a true immortal. Associated benefits of his godhood also include an armory of miraculous weapons including the unbreakable Shield of Perseus, and arrows dipped in the blood of the Hydra which can pierce through any barrier.
6 Spectrum
Monica Rambeau, the former Captain Marvel, is remarkably dangerous for a superhero who has usually been relegated to supporting roles over the last couple of decades. For example, her ability to manipulate energy has rendered her immortal.
Her power to control virtually any form of energy she encounters, including gamma radiation and cosmic rays, allows her to project destructive energy blasts. If that wasn't enough, she can assume forms of pure energy, making her intangible for up to several hours at a time.
5 Forgotten One
The Forgotten One is the outcast Eternal known as Gilgamesh, who throughout Marvel's history has served as the inspiration for many of the great heroes and epics of ancient civilizations. While not a true immortal like Hercules, his Eternal heritage has granted him an extremely long life-span and superhuman endurance.
During the thousands of years that he has roamed the earth, he has mastered pretty much every form of combat that the world has to offer. He is the strongest of the Eternals, and his strength is great enough that it rivals that of Thor and Hercules.
4 Moon Knight
With an array of high-tech gadgets and weapons provided by the Cult of Khonsu, his combat experience, adamantium kevlar armor, and mastery of numerous fighting styles and disciplines, Moon Knight is one of the most potentially lethal vigilantes Marvel has.
His "erratic" (to put it lightly) mental state has given him a ridiculously high tolerance for physical punishment and a unique style of combat that is almost impossible to replicate. He also may or may not operate with the mystical blessing of the Egyptian god Khonsu, it's not quite clear.
3 Ghost Rider (Robbie Reyes)
When all you see them do is ride around on flaming vehicles and give crooks penance stares, it becomes easy to forget just how much power the Spirit of Vengeance has. Take Robbie Reyes for instance: when the young Ghost Rider isn't cruising around in his Hell-Charger, grappling with his path in life and his role as an Avenger, he occasionally gets to unleash his spectacular abilities to their full potential.
The best example would be when he took possession of a fallen Celestial, turning the deceased alien into a towering, Hell-powered, juggernaut. This level of power is a common attribute to those who are bound to the Spirit of Vengeance. In the "World War Hulk" event, Doctor Strange claims that previous Ghost Rider, Johnny Blaze, is one of the few beings with enough mystical power to stop the Hulk.
2 She-Hulk
While Jennifer Walters may not be quite as strong or angry as her cousin Bruce Banner, she's still a Hulk. Where raw strength is concerned, that fact will always put her head-and-shoulders above most of Marvel's superhero community.
With hand-to-hand combat training from Captain America, and her ability to retain her intelligence when Hulking-out, She-Hulk is a formidable brawler when going up against power-house threats. Even though she has been gravely wounded several times, due in part to her high healing factor she also holds the distinction of being one of several major Marvel heroes who hasn't ever been killed in the line of duty.
1 Prince Namor, The Sub-Mariner
Imperius Rex! Prince Namor is considered to be one of the first mutants of the modern age and has an array of abilities stemming from his unique human/Atlantean heritage. He can telepathically communicate with most forms of sea life, swim at incredible speed, and has displayed a sort of hydrokinesis (the ability to control water).
On land, he is strong and durable enough to hold his own against Thor and Captain Marvel. In addition to his flight capabilities (the little wings on his ankles aren't just for show!), this makes him alternatively a dangerous foe or valuable ally. A side-effect of his hybrid genetics, however, is that oxygen imbalances, occurring from his constant moving between land and sea, give him serious mood swings, which account for his famously mercurial temperament.