I have the last two and have glanced through the first one. Comrie describes some fifty languages in detail whereas the last two describe languages by geographical area and genetically, choosing few languages from each region and describing important/interesting linguistic features of those languages. Both books might appear to cover the same ground but I think they actually complement each other. As noted, Comrie is quite expensive and I wasn't able to find a good copy for a reasonable price when I searched last. There will be a
new edition of Comrie in April, this year. It's difficult to choose one book to recommend because all three books are good and also because they are different in their approach and content. But if you wish to have one book, I would recommend the last book.
P.S. A basic knowledge of Linguistics would come handy (maybe even necessary) when reading these books.