which monitor calibration system to buy?

Hi I've been investigating buying a monitor calibrator for my Dell2209WA, but I'm having trouble distuingishing betwen the various manufacturers and models. The reviews I've found don't seem to compare or contrast what each one does and how well it does it. Also, for example, Spyder elite 3 and Spyder pro 4 and 4 elite all seem to be on sale at the same time. Colour Munki have the Display and the i1 Display Pro and I'm not sure (other than price) what the difference is between them. As you can tell I'm a beginner at this, so would be grateful for any advice or direction to a comprehensive comparison between the various options. Many thanks in advance John