1. The Dress Watch
I'm starting with the Dress Watch because this is often the watch considered synonymous with the "nicest" or "most expensive" watch in your collection, though this need not (and perhaps should not) be the case. To begin with, in the most formal of situations (e.g., black-tie formal), wearing a watch may not even be appropriate. Or if you absolutely must have a watch on-hand, a pocket watch is actually the dressiest option. A watch on a leather strap is usually considered dressier than one on a bracelet, and the simpler the watch dial (with fewer complications), the dressier, though applied indices (separate pieces affixed to the dial) may be preferable to painted ones. Traditionally, this meant an hour hand and minute hand, and nothing else; even minute markers were often omitted. A quintessential example is the Jaeger-LeCoultre Master Ultra Thin or the Patek Philippe Calatrava. Precious metal cases were the norm 50 years ago, but increasingly relaxed standards of dress, the popularity of steel cased watches, and the ever inflating price of gold, it's not as much of a requirement these days. Smaller-sized watches, both in diameter and case thickness, tend to be dressier since they can fit better under the cuff of a dress shirt. The only hard-and-fast rule of the Dress Watch is that it not be a digital watch (though some might make the case for a horological masterpiece like the A. Lange & Sohne Zeitwork, I'd hazard to say that it's a bit too big and complicated in its digital mechanism to qualify as a dress watch), and that it not be on a rubber strap.
My Dress Watch: Nomos Tangente Gangsreserve
Though I sometimes make it a little sporty by pairing it with a steel stretch bracelet repurposed from a Hamilton Ventura
(The other three essential watches--and one more--after the jump!)