I guess it really depends on your lifestyle. If you time stuff CDTs and stopwatches are nice. The exact features depending on whether you are timing a NASCAR race, a chemistry experiment or how long to roast your coffee...;-)
If you're doing outdoor things, compass/baro/thermo is handy.
If you need anywhere access to various 'data' something that records and displays that is great.
For me, it's really just time. I want accurate time and day/date. The features that enable that, for me, are solar and atomic. With those two features, the right display and a comfortable wear, I'm happy. Specifically, for me, that is a S/A Mudman 9010. Unbelievably comfortable with the "right" display, accurate, tough and "waterproof". What more could I want?
Okay, rereading that, I guess I REALLY need to list in order the things I like/want:
Comfortable to wear (for me, that is a large strap and light weight)
Accurate (atomic! Why pay some Swiss guy $1,000s to make a piece of machinery that will be ALMOST as good?)
Great display (day/date/time and easily readable - here I've decided digital beat analog - though I enjoy the looks of analog watches)
Low maintenance (waterproof/solar/tough)
Illumination (for the display, reading light brilliance is not required)
While these are in order, I don't have to choose between them and, having owned my Mudman, I never would.
+1 for solar/atomic. One of my G's is always my go-to watch when I know I have many appointments and deadlines on any given day. I save the automatics for the weekend when a few minutes or seconds shouldn't really matter b-)
If it does not have to be a G-Shock, I would also highly recommend looking into the Protrek/Pathfinder series. Definitely the most feature-rich watches in the Casio family, and arguably in the watch world.
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