I just started re-reading the series after running out of things to read. I like all 6 books in the series for different reasons, although my 3 personal favorites are The First Virtue, Vectors, and Quarantine, primarily because I love the DS9 and Voyager crews, and because TFV (which, incidentally, I decided to read first) has a really interesting cast of charaters (and makes me really want to read the Stargazer books, although I don't know where I can get my hands on them).