This is the 'heart' of the watch and it all depends on what and where would you wear the watch and what are your habits. A good watch is a running watch, just like a car and motorcycle.
Mechanical watches - These are the traditional watch mechanisms that require you to manually wind up the watch everytime you wish to wear it. Once wounded up it would typically last about more than a day. Choosing this type of engine would mean that you would have to wind it a few turns everyday before you wear it. No batteries required for these watches but diligence and discipline is a must.
Mechnical watch IWC
Automatic - These watches are the same as mechanical but a semi circular weight or rotor disc to wind the watch as you change the orientation of the watch (wrist movements, walking, driving etc). Thus the name 'Automatic' as you would automatically wind the watch while you are wearing it. The power reserve for most automatics are usually about 40 hours (Some seiko's can last for 50 hours). Choose this watch if you would wear it daily. Automatics have an advantage of never having to replace any batteries and thus never having to open up the watch making the Water Resist seals intact and making these watches last a lifetime. I personally have worn a vintage seiko that was made in the 1980's and its still ticking and keeping time :)
Automatic with Manual wind and Hack - Same as the above but the crown can also be used to manually wind the watch. This is best for those wish to collect automatics as they can manually keep their watches running wihtout having to wear it. Hack here means that the the second hand can be stopped while adjusting the time. Most automatics do not have a hack feature. Useful for those who have OCD and must have their watches synced and accurate to very second. Automatics and mechnical watches have sweeping second hand motion which adds to their appeal.
Seiko's proven 7S26 movement. Reliable and tested.
Quartz Analogue/Digital - Quartz was the modern technology of watches, and uses a quartz crystal and piezo-electric to regulate time. One of the strong points of a quartz watch is its accuracy, with +-15 seconds. You can usually tell that a watch is using quartz movement by looking at the second hand as it will move in segments or "tick-tick" motion. Quartz watches are also usually "loud" so its not a good option for those who sleep with their watches. (quartz digital is quite though). Battery life for quartz watches go from 1 to 3 years. Some Casio digital watches boast a whopping 10 year battery life.
Quartz Battery Powered. Accurate!!
Kinetics - Kinetic watches was an atempt to combine the best of both worlds of automatics and the accuracy of quartz. Basically its a quartz watch that is powered by a dynamo which is turned by the rotor disc. Power generated by the rotor was stored using a capacitor and then later rechargable batteries. The early capacitors were a bit of a failure being unable to store charge after a while. Kinetic watches will eventually have to replace the batteries and replacement batteries are not as cheap and easy to obtain compared to standard watch batteries.
Breakdown of a kinetic movement
Solar - Solar technology is one of the newer tech and powers the watch by converting light energy into electirical charge. With this you get the accuracy of a quartz watch and you can keep your watch running without having to wear it. Just keep them under some light. The life of these watches vary from 6 months to a year (without light mind you). Solar powered watches are available from Casio, Seiko and Citizen but among the three, its Citizen that is pushing this technology with their "Eco-Drive" watches. Casio calls it "Tough Solar" and Seiko simply calls it "Seiko Solar". Choose for the environmentalist in you :)
How an Eco-Drive works
Chronograph movements - Many often confuse between a chronometer and a chronograph. A chronometer is basically a device tells time (clock, watch) a chronograph is a device that can measure time (stopwatches). I will explain about various chronograph movements at a later time. Although most find that they rarely use the stopwatch feature. its useful for those who time their runs, or do simple calculations, or even for examinations.
Special Movements - Some watches have other special movements like a an alarm function, world time, compass, thermometer, perpetual calender (automatic monthly date change 30th to 1st) moonphase etc etc. The more features means the more power required to power the feature so usually these special movements uses quartz and are battery powered. Timex has a watch that has a compass, thermometer and tide graph all built into and analog display. These are the swiss army knives of watches and would appeal to the gadget lover and outdoors man. You pay a premium for each feature you get.
Timex Expedition. Full of gadgetry.