It's possible the press would not portray his trial fairly, but the proceedings are public, and a trial would draw continued press, whereas if Snowden successfully seeks asylum, the story goes cold.

I should elaborate on Snowden's choice of helper countries: is a national security risk to the United States. Here you have someone in possession of state secrets who needs help from a foreign government. That's the definition of compromised. What is he going to trade for protection? More classified information, of course--possibly much more sensitive information than the relatively harmless, widely known) programs like PRISM. He has national security information, and foreign governments want it. This information will eventually flow to the intelligence agencies of China and/or Russia.