Although dive watches are great, since they have a simple count-down bezel and are pretty robust, id have to say an alarm is the most important thing if your doing bush work to wake you up in the morning or remind you of the next flight etc.
The rest of the typical magazine-ad giant watch with slide rule functions is for people who like dressing up as pilots and thinking watches attract women in bars (as some numb-nut recently posted).
Rolex watches are OK but they lose time and are made for wankers who believe 007 exists and wears the same watch they do.