I hate having the same opinion as most people but in this case most people are correct.
There are soooo many Avengers and the most poworful is Thor by popular consent (and in my opinion).
Thor odinson the prince of Asgard, bane of Celestials, killer of the Sentry, injurer of Galactus, and God of Thunder is 24 time stronger than Wonder Woman!!! 24 times! (see evidence in Mark Specter's answer to Who would win in a fight between Wonder Woman and Thor?) Who has contended with Superman and Martian Manhunter, he has knocked back the Phoenix and fought it all the way back to earth, and he has split the scull of a Celestial. He can travel hundreds of time the speed of light and his battles with similarly powerful beings span galaxies! He even absorbed to power of the Godbomb a devise that was meant to kill all gods who had ever lived through the time stream and Survived!!!
Thor is the god of gods and is truly earths mightiest hero.
The three other major contenders for this title are the Incredible Hulk Dr. Strange and Scarlet Witch. All are incredibly powerful but none compare to the god of thunder. The Hulk is stronger than Thor and arguably more durable but in all other Than that he is infusion in all respects. Then there’s the Fear itself fight with an amped Hulk and Thing Double teaming Thor and him defeating both of them. Fear itself is one of the only times Thor was pushed to his limits on earth.
So Hulk is powerful enough to be a challenge the Thor but nothing more. Scarlet Witch has some impressive feats but many people don’t know that in Avengers vs X-men her power was super effective against the Phoenix Force and During House of M and Avengers disassembled she was heavily amped by Cthon and life force and her next best feat is actually her slowing time down and removing Thor from the battlefield temporarily. The narrorator even states that she knows that she is incapable of beating Thor so she tries this.
So Wanda is less powerful but again, still a challenge. But one person defeated Wanda Maximoff even when she had the Cthom and life force amp and that person has the best chance at dethroning Thor as the most powerful Avengers…
DR. STRANGE! This character had one shotted clones of both Hulk and Namor (though it is unclear how powerful they are in relation to the real ones) he can fly at the speed of thought, is capable of resurrecting the dead, and Classic Dr. Strange is the most powerful avenger as he defeated Dormammu but he is not around anymore and so strangers best feat is still defeating house of M Scarlet Witch:
So Dr. Strange is a fraction of a percentage lest powerful than Thor and the God of thunder reigns supreme. But now that their both on the current avengers roster this is one of the most powerful versions of the Avengers!