Square Enix reveals lifetime sales data
According to Square Enix the Tomb Raider series is their best selling franchise. In total 30 million copies have been sold. The first game sold about 8 million units but since then the sales for every successive game have constantly declined.
Another important franchise is the Hitman series which sold about 8.3 million copies, whereas Hitman 2 was the highlight with almost 4 million units.
The Deus Ex series sold about 2.4 million copies - the fourth place is Kane & Lynch which was sold 1.7 million times.
Take a look at the original Square Enix figures below. Unfortunately they do not say how many console and PC units were sold in each case.