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?