I’ve written two books: For Individual Rights (FIR), originally published July 2010, and REASON and LIBERTY (R&L), originally published July 2013.
R&L is more philosophically rigorous, covering fundamental matters such as “metaphilosophy”, the nature of reason, metaethics, the intimate relations of reason and liberty, and a brief philosophy of institutions. FIR is squarely focused on political philosophy.
Some people seem to prefer FIR, while others prefer R&L (I myself prefer R&L). If your interest lies mainly in ultimate justifications of things (i.e., if you tend to be quite philosophical), then I would suggest starting with R&L. If it lies mainly in characterizing what liberty means, then start with FIR.