In terms of technology and metrics you'd be looking at probably these guys:

http://www.mybasis.com/

These guys received indiegogo funding but havent' launched yet: atlaswearables.com

My company specializes in Internet of Things predictive analytics. "Internet of Things" includes wearables, so we closely follow this market.

This market is constantly changing. You'd need to better define what you mean by best. Is price a major consideration, or is your main concern having access to the data? Does it absolutely need to have a heart-rate monitor?

If you had asked six months ago, and ignoring the data openness issue, the various wrist-wearable Fitbit models, the MisFit Shine, Nike Fuel, and Jawbone models would all have been strong contenders on price/performance measures. The BodyMedia offered a heart-rate monitor, but received poor reviews and complaints about the monthly subscription fee as well as the bulkiness of the product.

Fast-forward a few months, and you have much better options for "inexpensive" heart-rate monitors that can provide completely open data and do so much more. Again, you didn't mention price. But the Samsung gear just came out with a smartwatch with built-in heart-rate monitor. It runs Android. With the right apps (and there are many), this should do exactly what you want. (It's sounds like you're pretty technical. Since this is Android, you can even write your own app to capture the data if absolutely necessary. You can't get more open than that in terms of data openness. With unlimited time or money you, or a contractor, can write your own app to make this fitness tracker do exactly what you want.)

Are the Samsung Gear models in your price range?

Of course, the iWatch is rumored to be coming out soon. It's not clear if it will include a heart-rate monitor or not, but it might very well. Judging by the reception other Apple iOS products have received, if this includes a heart-rate monitor it will likely be close to the "best" one available, at least judging by market acceptance. You'd likely have a huge selection of pre-existing and free fitness apps to chose from. If you're technical or have access to technical resources, custom coding is also open to you.

I'd be more than happy to take more about wearables and the Internet of Things, as well as predict analytics for fitness, air quality, environment, and marketing. Feel free to set up a call using Clarity.

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/