Having read a number of books and articles on the Qabalah, many of them have significant failings or omissions. Some of the older works focus on a particular book or on the theology, rather than practical work with the Tree of Life. If you like scholarly styles of writing, then Mathers and Levi may appeal, but I prefer a more readable and pathworking-focussed style, to accompany direct tables of correlations such as 777.
Fortune's Mystical Qabalah is probably the most complete and workable book that I had read to date on the Qabalah and the Tree of Life, and for rituals based on Qabalistic principles, then the Golden Dawn books and texts are also interesting.
If you've read something (or quite a bit) about the Qabalah, and want to learn more, then Climbing the Tree of Life will be of great value to you - it illustrates various concepts which I had not seen mention of in Mystical Qabalah, Golden Dawn teachings, etc, such as straightforward discussion of Daath, the 7 Palaces, the 5 Adams, etc.
There is little reason not to start with this book if you want a broad-reaching, lucid understanding of the Tree of Life, as it covers many concepts while remaining clear and practical.