Going to reiterate what everyone else has said, but...
Both methods have their merits, but as a rule I like my students to use the fractional method, simply as it needs less brain power. On long legs though, as said by WWW, especially if it is rather featureless the time method always works well. Though I always like my students to mark a positive fix on their map including a time no matter which method they are using. It helps if it all goes T*ts up later on.
One way of making Nav seem less daunting to most people may seem strange, but getting studes to practise mental arithmetic seems to make a big difference, especially when calculating ETA's. I'm amazed how poor most people's mental calculating power is and that it really can be a stumbling point, as they spend so long worrying about it that everything else goes out the window!