i am currently translating the extant works of Catullus, in aid of which i have 6 different translations. Peter Green's is the one that is indispensable, as well as the most pleasurable to read for its own sake.
for example, on the page facing his translation is the Latin text, a sine qua non for appreciating Catullus's brilliance.
there is also a glossary that explains the significance of each proper name to the poem in which it appears. and, most helpfully, there are notes to each poem that summarize not only Green's wise interpretation, but various views by other Catullus scholars.
the translation itself strikes a perfect balance, to my taste, of the literal Latin, Catullus's meaning and intent, and elegance (without stuffiness or pretension).
if you are going to buy only one book of Catullus's poems, or are thinking about adding to your collection of them, this is the one to get.