I usually don’t take phrase books, but some basic advice:
Unless you’re spending a 2 or 3 weeks or more in one country and will be doing “living there” things like shopping for groceries and household supplies, I think I’d go for “all in one.” You’ll probably only need the basics for ordering from a menu, buying a train ticket, etc. You don’t want to be lugging around a lot of books. Go for whatever combination of book/books is the lightest and least bulky.