No, the Writings are not an anthology, they are a part of the frustrating publication history of Trotsky's work. If you want to give someone a single book, get them The History of the Russian Revolution. It's a masterpiece.
For the most part Trotsky's writings are scattered through 20 some odd books, plus a 14 volume series of writings. How it was done is ass backward: articles were collected topically and everything from 1929-1940 that didn't make it into a collection was put into the Writings series during the '70s. So for instance, although Whither France? was written in 1936, it is neither in the 1935-36 volume nor the 1936-37 volume, but instead in Leon Trotsky on France, a collection of Trotsky's writings on France (but not his writings on the dispute in the French section of the International Left Opposition, which are referenced in the ... On France writings but are in another book, Crisis of the French Section). The pre-1929 stuff is even more frustrating as it's sporadic what is even in print.
Rather than subject whoever this is for to all that, get the History. They'll appreciate it.