Take a look at the specifications for the regular Blue drive and the Caviar Blue version you're looking at. Chances are the differences will lie in either the RPM, the cache size, or the SATA type, or more than one of the above. But to muddy things further, there may be more than one Blue or Caviar Blue model of the same capacity, each with different specifications.
Just as an example, this Blue and Caviar Blue model are both 1 TB, both SATA 6GB/s and both have a 64mb cache, but the Blue is 5400 RPM and the Caviar Blue is 7200 RPM (and therefore, of those two drives, probably the one you'd want.)
https://pcpartpicker.com/product/q3Z2FT/western-digital-internal-hard-drive-wd10ezrz
https://pcpartpicker.com/product/MwW9TW/western-digital-internal-hard-drive-wd10ezex
But, if you look through the drives in PCPartPicker, there's another Caviar Blue 1TB available which has only 32MB cache, but for some reason is more expensive than this one! Confusing!