Haven't messed much with viewers. If you can google up a copy of the old 3dExploration demo, it's probably the best viewer/converter around. The demo has a nag screen but it doesn't expire. Of course, you're on your honor to purchase the full version - now DeepExploration I believe and not real cheap.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken