I have a Polar F6 and love it. It syncs up with the cardio machines at my gym, which is a plus.
As for accuracy -- HR monitors are very accurate reporting your heart rate. For calories burned, monitors use a generalized formula to calculate calories based on your heart rate, given your age, height, weight, and gender. So it's only an average for women who are your age, height, and weight, with your heart rate. Unfortunately, they can't directly measure how many calories you're actually burning.
Even though it's only an average, I find the calories burned on my HR monitor to be much more plausible than the ridiculously high number given on the cardio machines. My elliptical machine told me that I burned 420 calories this morning in 30 minutes; my HR monitor told me 248. I think the HR monitor may still be a little high, but much closer to reality.