As an avid self-tracker/QS devotee, I have evaluated pretty much every fitness tracking device out there, and while each has its pros and cons, I have been happily using a Basis (http://www.mybasis.com/) as it has the most comprehensive set of features out there (heart rate, GSR, calorie expenditure, sleep and activity tracking).

However, I was frustrated that they didn't provide a public API or a way to download my data, so I wrote a script that will download your data - http://www.quantifiedbob.com/2013/04/liberating-your-data-from-the-basis-b1-band/ .

Note that all devices will have accuracy issues, whether it's tracking steps or heart rate. And I have yet to find an accurate way to get heart rate variability other than via a chest strap, such as the ones made by Polar.

Another one to check out is BodyMedia (recently acquired by Jawbone), which is considered fairly accurate but you need to wear it around your upper arm - http://www.bodymedia.com/