Interesting question, which I’ve had to consider for a while.
One of the joys of my work is I get to read a whole slew of interesting research and information in areas as varied as biblical research, social work, history, psychology, and the law—and people pay me for it (well, after I translate or edit it, of course).
So if I had to choose a favourite, it would probably be one of the books that I’ve translated that was on a fascinating topic and taught me a great deal. The following three are very compelling candidates: