I don't have much to say on the Manning conviction because Joshua Foust said damn near all of it so well here. For me, the key really is how indiscriminate the dump was. Had Manning released a few key documents that revealed illegal or even just poorly conceived American programs, then a whistleblower he might be. But that is not what he did. Instead, he collected as much stuff on anything and everything and then handed it over to someone else to release, which was lazy and irresponsible. It is not whistleblowing but something else. And in the process, he broke a variety of laws. He should not have been treated the way he was once he was arrested, but that does not mean he did not commit some crimes.
I have similar feelings about Snowden, as he released some information that probably needed to be exposed and much information that did not need to be exposed. More damning is the timing for Snowden--contacting the media and then getting the NSA contracting job--that it was deliberate ... espionage.
Anyhow, I am not a legal analyst, and I have not followed either of these stories as closely as others. Josh did a great, nuanced analysis on Manning--that his superiors screwed the pooch on multiple occasions, but that does not absolve Manning of responsibility. So, go read Josh's piece.