For the clear majority of my life, I've keep my wrist naked of any ubiquitous time telling device and have been very happy with that sense of freedom. A couple of years ago however, I surprised myself and bought a watch. There were a couple of reasons for doing so, but the main one was to improve my exercising. For a year or two prior to that purchase, I went through the hassle of wearing a pulse strap and a small android device (without a sim-card) whenever I went running.
As my primary reason for getting a watch was to collect heart rate data, there were not too many brands available on the market. A requirement of mine was to be able to keep my measurements private. While Apple, Withings and a bunch of other brands might offer products having functionality, to the best of my knowledge, Garmin is the only manufacturer who also meets the privacy requirement. Garmin of course has optional bluetooth cloud connectivity and such, but their products also work in disconnected mode as regular USB storage devices. Steven Maude has written a post on Using Garmin watches with Linux which helped me getting started. While shopping for my watch I got the impression Suunto might make neat technology, but couldn't find any indications that anyone had managed to get data off their devices using free or open software. Please let me know if you know that to be possible.
Some people (understandably) confuse sports watches with smartwatches. Thus as an ending comment I feel a need to clarify that Garmin watches typically have a battery life close to a week, as opposed to merely a day or two.