What do you think ?
The material Petraeus handed over included, by his admission, information of the highest top-secret status. In intelligence terms, a treasure trove, and its public disclosure would have been ruinous to the USA's interests. Fortunately, none of it was ever made public. As for Petraeus's motivation, well, it was personal gain of the basest kind. He certainly didn't suggest he was acting in the public interest.
There's a second difference between these cases. As noted, Manning got 35 years and Snowden faces 30 years if the Americans ever get their hands on him. Petraeus, by contrast, has reached a plea bargain with US prosecutors under which he will plead guilty to a misdemeanour with a recommended penalty of two years' probation and a $40,000 fine. No jail time.
http://www.abc.net.au/news/2015-03-04/bradley-petraeus-plea-deal-shows-bizarre-double-standard/6280708
Handing over top secret documents is a crime be to a web site or a bed partner. Some US politicians wanted Assange to face the death penalty and he did not hand over secret documents but merely published them. Broadsheet media also published the same material yet did not face the same hostility. Snowden and Manning never profited from their leaks yet one is doing 35 years. Strange world.