Voted SPR and American Beauty.
Lebowski is more rewatchable, but SPR gets the vote based solely on the technical achievements. Yeah, some of the acting was stilted, and yeah, some of the plot points were stereotypical "war movie by the numbers" fare. But so what? The plot and the acting were secondary to the directing. And Spielberg nailed it.
I could do without the heartstring-tugging scene at the end (in the cemetery), however. That moment seemed like cheesy filler that was added by executives in a boardroom after seeing negative feedback cards from an ignorant test audience.
As for the other movies of '98:
The Truman Show: great movie, but a little too "popcorn" to be an Oscar contender. Plus, I don't think that the Academy understood that it wasn't really a comedy.
American History X: too violent. No way the Academy would ever celebrate a movie like this.
Rushmore: I think it's too much of a comedy to be Oscar-worthy. And it's a little too quirky. Also, a lot of it just seems like an excuse to let Murray improvise.
The Thin Red Line: war-movie-by-the-numbers.
Shakespeare In Love: great acting and a fun, breezy plot. But ultimately forgettable. One of the least-deserved Best Picture winners in the history of the Oscars.
For '99, I think it's pretty clear that The Matrix and Fight Club split votes among the "pro action" members of the Academy, which resulted in a win by American Beauty. And I don't mind that at all. I think AB is a classic "adult drama" with superb acting by everyone involved.
The Matrix has certainly been a bigger influence on moviemaking over the past 20 years. But movies with lots of action and a confusing plot just aren't going to win the Best Picture Oscar.
As for the other movies of '99:
Magnolia & Being John Malkovich: too weird.
Sixth Sense: the twist ending makes you want to watch it a 2nd time, after which you realize that it's actually not that great of a movie.
The Insider: it's the kind of story that plays better as a documentary. All of the drama and the tension and the climax felt fake and manufactured.