You really think Reagan, McCain or either of the Bush presidents would have been more lenient on him than Obama? (I'm not being pro-Obama, just realistic)
But, they are not remotely equal, because Obama is an outgoing president with no more elections to face. There is virtually no chance that any candidate for president, or president who will be a candidate again, could pardon Snowden.
Snowden is a true American hero, but most Americans don't understand what he did. Most also believe that illegal domestic spying is acceptable if it's "to fight terrorism"[1].
Politically, it would be suicidal to pardon Snowden. Obama doesn't have to worry about that anymore, so Obama is basically Snowden's best and only hope of that happening.
(It still won't happen, though.)
[1]; http://www.people-press.org/2013/06/10/majority-views-nsa-ph...