There you have the question and I'm looking forward to your opinion!
Do you think that Thor is really worthy of wielding Mjolnir? I personally don't think so. Looking at the character and the way he behaves nowdays and how he treats not only opponents, who are less powerful than him, but also people who are somewhat close to him, I don't feel like it. And the same applies for Captain America. Not for the same reasons, but I never felt like Captain America should be able to wield Mjolnir. Yes, he has a noble character and always does the right thing, but I don't feel like his adventures and moments have backed it up enough.
The only well known character in Marvel comics, who is worthy of wielding Mjolnir is Peter Parker aka Spider-Man, in my honest opinion. I feel that Peter Parker went through so much depressive moments and always came out of top. Not because he is supposed to be the all-american superhero, or a very powerful Alien from some weird dimension, but simply because he is an amazing guy, who is always looking forward to the next day, no matter how dark it gets and how much **** he gets from certain characters and since we're talking about Spider-Man, it's basically all the people in New York, who gave him shit on a daily basis.
I'm really waiting for a brave writer, who thinks just like me to see a scene in the comics, where Odin kicks Thor back to the stone age, looks at Spider-Man and yells something like: "YOU ARE WORTHYYY!!! YOU ARE MY REAL SON, PETER PARKINSON ODINSON!", and then he gives him the Hammer and Spider-Man gains more power than he had for a while as Spider-Universe.