At this point, Snowden is a pawn in an international strategy game. None of these countries are offering Snowden asylum because they believe in his cause. They are offering him asylum because it is something that they can use against the United States (for unrelated contentions) and use as a political trophy within their own countries.

As such, Snowden has to worry about many scenarios. Will his "host" country use him to extract concessions out of the United States in exchange for his extradition? When the regime changes in the country he ends up in, will he wear out his welcome? Can the country he ends up in even protect him from extraordinary rendition? Even if the country fully intends on assisting Snowden, would it be able to weather whatever sanctions were levied on it by the United States in the form of trade restrictions? Ecuador didn't seem to think so.

Then there is the question of whether he can even get to the country he is going to. France and Spain (indirectly) forced down the jet of the president of Bolivia on the rumor that Snowden was on the plane. There is no reason to expect that they and other European countries won't do so again. Routes from Russia to Cuba (assuming he has to use Havana as a stop) also typically fly over the United States. The United States is free to, if not directly force the plane down in the United States, not grant it permission to fly in U.S. airspace, effectively forcing it to land in a U.S. friendly country (Canada). And Cuba might simply hand him over to improve U.S. relations. My understanding is that small private jets simply do not have the range to go directly from Moscow to any of the countries listed (perhaps Venezuela would be just within reach).

At this point, though, I don't really see what option Snowden has but to take Venezuela's asylum offer and hope for the best. He is on a small boat on the ocean in a raging storm. His fate is not in his own hands.