Which translation of The Prince you should read depends on your criteria for a translation, which are not specified in the question. Readability? Closeness to the original? Quality of annotations (which are absolutely necessary for most readers, unless they are well-versed in the history of Italy in the 15th and early 16th century)? Language? (Swahili, Chinese, Rhaeto-Romance, Esperanto?)
Let me assume you are looking for an English translation. The translation by Peter Bondanella (Oxford University Press, 2008) may suit you because:
- It is the first translation based on the authoritative Italian text edited by Giorgio Inglese (1996). It is possibly still the only translation based on that text.
- It has an introduction by Maurizio Viroli, a renowned expert on Machiavelli, that puts the text in its wider context. (Viroli has published many books on Machiavelli, including a very accessible biography.)
- It has endnotes that explain names and events (especially from Machiavelli's lifetime) that most readers will not be familiar with.
- It has a list of names of historical figures that are often mentioned in the text.
- It has a section with further reading that is not simply a list but that explains which books would match which types of interests.