Traveling to Prague, Budapest and Croatia

The only RS book I have is the Budaprst book. It's very okay for planning. There is another brand that is also very good, especially for use while traveling.

You don’t say how long you’ll be in Prague, Croatia and Budapest. And that does instruct any meaningful replies you might receive.

I suspect what kenko is getting at is what is written in website. https://store.ricksteves.com/shop/p/eastern-europe-guidebook. For instance for Budapest it says:

"Should I get Rick's Budapest guidebook in addition to this Central Europe book?
If you're spending only a few days in Budapest, Rick Steves Central Europe is all you're likely to need. If, however, you're spending four days or more in Budapest, or at least a week in Hungary as a whole, the extra information in Rick Steves Budapest can be worthwhile. It offers more in-depth sightseeing information on Budapest, several additional self-guided city walks and museum/sight tours, and more specifics on shopping and entertainment, plus activities for kids. It also includes all of Rick's favorite Hungarian destinations outside the capital, plus nearby Bratislava."

Similar advice is gven for your other stops.

Prague, Budapest, Croatia is a pretty large region. Unsolicited suggestiion; fly Prague to Budapest and Budapest to Podgorica .... or reverse. You will have to plan a bit around the days of the week the discount airline flies direct to Podgorica. And if that is your plan I would get individual books as the Central Europe book, at the expense of detail in Prague and Budapest, covers a lot between the stops that you will be flying over.

If you are going to drive it, or if you are going to do a lot of day trips, maybe the Central Europe Book. As a guide while on the trip, DK Eyewitness Top 10 for Prague and Budapest is a good idea regardless of other choices.