Watches are extremely important for a pilot, especially small aircraft that do not have sophisticated instrument clusters. Everything is time-based and generally it is much better to trust your own watch than one built into the instrument cluster (unless it is a high-precision, calibrated clock on a large aircraft). Also, if anything happens that disrupts the aircraft functions or your visibility of the instruments, a watch is critical. For example, a fire or power failure can make a panel clock unlighted or obscured. Also, you may not be in the cockpit/flight deck and need to know what time it is.
The key factors for a "pilot's watch" are:
illuminated/visible in darkness
large numerals, clear and highly readable
ability to manage multiple time zones easily
24-hour (military/zulu) display capability
day of the month indicator
rugged and water resistant, tough crystal, good quality construction
Currently I use a Torgoen T05101. It is a good watch, but uses phosphorescence. My next watch will use tritium illumination.
I have been known to use an egg timer in the cockpit.