Starship Troopers Book (1959) or Movie (1997)
Nearly every component of what we recognize today as "sci-fi" was present in this masterpiece. The groundbreaking book preceded Star Trek by nearly a decade, yet here we have giant starships traveling between worlds. Space Marines and battlesuits, as we know them today, would not exist without Heinlein's imagination of Johnny Rico's "Powered Armor Exoskeleton."
Warhammer 40,000's Space Marines owe a debt of gratitude to Heinlein as well, having conceived of the capsule trooper ("cap trooper"), though he also deserves some credit for one of the 40K's Tyranids with the "bugs."
Compared to the movie, the book is much deeper, and delves into issues that are still controversial today. One of the criticisms of the book is that it was seen as a vehicle for the author's political views. An important point of the story is defining the difference between a citizen and a civilian, and the benefits of "service." Certain rights are only extended to veterans, and they are also given special dispensations after they have completed their 2 years of service. Allegations of militarism, and even fascism were even leveled against him. Parallels to the Third Reich were made. Heinlein, to his credit, said that he based a significant amount of the book on Switzerland's system. The book currently resides on the required reading list for the Marines and the Navy, and has previously been on all 5 services reading lists.
The movie, on the other hand, is very good, but fairly light in comparison to the book's deep undertones. It is an enjoyable romp through space and on various worlds. Some of the issues are addressed, but not nearly as articulately and completely as the novel. There is also a bit of humor in the movies, including some tongue in cheek commercials.
Overall, I would recommend both the book and the movie. What I can honestly say about both book and movie is they are both excellent. Too many times the movie falls short of a wonderful book. Rarely the movie is better than the book. Rarer still is a book and a movie that seem to complement or even stand alone individually. It somehow manages to be one of those stories that works both ways. But understand they they are two very different forms of entertainment.
If you want to sit and enjoy a ride through strange worlds, battling insect-like bugs - go for the movie. If you want to sit down and enjoy a well-written novel about the military that makes you really think, and address some issues, the book is the way to go.
I have enjoyed both thoroughly.