I have been using Nextrend for a few months now, and have found it to be very reliable. It does not seem to use as many resources as other services I have used in the past.
The data has been accurate so far and the tech support is second to none. You will usually get to speak to somone live within 30 secs and if they tell you that they will get back to you, they will.
We all have different needs, but for me reliability and ease of use is important.