tolkiens legendarium - What was more powerful - the power of the ring or the willpower of Gandalf and Aragorn?

I have not read the book but have seen the movie.

The ring almost tries to possess everyone like Boromir, Sam, Gollum, Bilbo, Frodo, etc. But why does it never affect Gandalf and Aragorn. Was it weak in front of them, or was their willpower very strong?

Answer

The way Tolkien describes the Ring it's clear that its effects are addictive. There is an initial temptation to use it, but to have the Ring fully take control of a user, the user must be in possession of it and have continued to use it for an extended period for it to have the full effect.

I'll refer you to Tom Shippey's The Road to Middle-earth for a more complete discussion of this observation.

The Ring actually does offer some temptation to Gandalf in the books (I can't recall if the same happens in the movies), as is described in Shadow of the Past:

'But I have so little of any of these things! You are wise and powerful. Will you not take the Ring?'
'No!' cried Gandalf, springing to his feet. 'With that power I should have power too great and terrible. And over me the Ring would gain a power still greater and more deadly.' His eyes flashed and his face was lit as by a fire within. 'Do not tempt me! For I do not wish to become like the Dark Lord himself...'

The reason why Boromir succumbed so easily is that he saw the Ring as a means of gaining power to defend Gondor; as Tolkien describes in Letter 246:

It was part of the essential deceit of the Ring to fill minds with imaginations of supreme power.

This same letter also provides an explanation of why others in the story also rejected the temptation of the Ring:

But this the Great had well considered and had rejected, as is seen in Elrond's words at the Council. Galadriel's rejection of the temptation was founded upon previous thought and resolve.

I'm not aware of any concrete explanation of why Aragorn rejected it; perhaps his friendship with Gandalf had given him the necessary knowledge of what to do, or perhaps it was the case that his main desire was for Arwen. Likewise I'm not aware of an explanation for Faramir's rejection (which is quite different in the books to what's presented in the movies).