Citing old or new papers of same work? Often researchers publish their work incrementally. Abstractly speaking, let's say, in 2010 the researcher publishes version 1.0 of his algorithm/system/framework. Two years later, he publishes an improved version 2.0 of the same algorithm/system/framework.

If I want to cite his work, should I 

a) cite his oldest work (advantage: typically, older works have more citations), 

b) cite his newest work (advantage: my readers will be directed to the most uptodate version of the author's work), or

c) cite both?
You might cite both by saying "Idea X, originally developed in [1] and extended in [2], shows that ..."