Which type of heart rate monitor is generally the most accurate?

Chest strap: You can research some consumer websites or even look at ratings for the one you might be interested in. Read some consumer comments/ratings. The most accurate type will likely be the chest strap, but I have seen ratings on some wrist straps which are probably just as accurate. The strap you use though must fit you correctly to be accurate.

I like : The omron wrist BP cuff because it is portable, and tells both BP and pulse.

Manual: The most accurate way is to manually feel your pulse and count the pulse over 1 minute, that gives you the heart rate. An electronic monitor will do the same. If you want to use an electronic monitor find the one that is convenient for you, any one you buy from a pharmacy will be accurate. The pharmacist can help you compare different models.