[neverending]

Can't vote in the poll because there is no "right" answer that would fit every film. It just depends.

A fine example of never showing the monster would be The Dunwich Horror. Though many view this as a cheesy low-budget affair, I quite like the way it portrays the cosmic forces involved by use of wind and fog and some psychedelic effects. I think it imparts what Lovecraft intended quite well.

There's much to be said for a sparing glimpse of the creature being much more effective than lingering for too long. Hammer's The Abominable Snowman of the Himalayas shows the monster for about 3 seconds, and it's a shocking moment in the film. More recently, The Descent used fleeting glimpses of the frightening creatures to great effect.

It's a rare film that can get away with not showing the monster at all and make it effective. The director has to really involve the viewer. Blair Witch Project and the first Paranormal Activity are two that come to mind, though audiences are split on whether those films worked or not. I think they did.