Snowden is a far better choice. He made a decision that can be debated. Is he right or wrong. If wrong was his action wrong or his intent? Was the government wrong?
But Manning is just a freak show. Nobody is saying he/she was right. In fact, the fact that he stayed in the news is his only interest. Most everybody agrees that he is a coward, a deserter, a person who endangered the other members of his unit. The fact, that he got the US government to pay for his costume change is not what most of us consider a Harvard education, but rather some National Inquirer expose. And maybe that is all Harvard is anymore, and A list of freaks entertaining Harvard undergrads.
In common law it is permissible to cause harm if your purpose is to prevent or end a greater harm. Kicking in the door of a hardware store to grab a gun in order to stop a rape was the example I was taught. In Snowden’s case he kicked open the door exposing the crimes our own government was perpetrating on all of us. He took a great risk doing this and sacrificed a lot for us. He’s a hero in my book.