From my limited experience, all the watches are fairly accurate in calculating your HR. Even the cheap off-brand one I picked up at a garage sale worked well. The big difference is compatability and features. When it comes to compatability, Polar is the king. If you do cardio work in a gym, chances are that the machines will read your Polar monitor. The same can't be said for other brands. As far as features go, I think other brands tend to beat Polar at a given price point. One of the things I like about the Nike watch you are looking at is its ability to display your HR as a percentage. That is a feature I wish I had on my current watch (a Timex). Things to look for:
1) Is the chest strap comfortable? Polar has some nice ones including a jogbra setup and a soft fabric band.
2) Is the battery user replaceable? Not all heart rate monitors have this feature, and it can cost $30 or so to replace a transmitter vs a few dollars to replace the battery.
Here is a short review for you:
http://www.lifestylemd.com/index.asp...d=714&typeid=1