Really it's personal preference. I know they do these surveys and come up with an answer from that, but the surveys can change depending on who you question. Might do a survey of 10,000 people and get 4,250 being a majority agreeing Pearl Harbor is the greatest war movie made thus far, then a year later do another 10,000 and they pan Pearl Harbor and say All Quite on the Western Front.
Me, Pearl Harbor's an ok movie, but I always tell folks if they really want a good movie on Pearl to ignore Pearl Harbor and watch Tora Tora Tora instead. To me Pearl Harbor is just another Titanic. The historical event is just used as a backdrop to get folks in to watch a romance, it's not the central focus of the movie. Change the backdrop without having to change the plot and it's the same thing. Tora Tora Tora is more focused on the event to me.
But that's just an example of personal preference.
No real clue what my personal best war movie would be. I'd probably go with:
how about the Alamo? Have ya'll seen the newer one with Billy bob thorton? IMO very good movie and for the most part historical. Also braveheart. But yeah saving private ryan would have to be the most realistic.
Interesting war movies, tho not all are near the top of my (or anybody's?) list:
Seige of Firebase Gloria (Vietnam, with R. Lee Ermey)
The Outlaw Josey Wales (Clint Eastwood, post-Civil War)
Stalag 17 (William Holden, WW2 POWs in Germany)
Caine Mutiny (Bogart as off-his-rocker WW2 destroyer captain)
Mr. Roberts (Henry Fonda as frustrated cargo ship quartermaster)
Last of the Mohicans (Daniel Day Lewis, Russell Means, F&I War)
Dances with Wolves (Costner "goes Indian")
Twelve O'Clock High (Gregory Peck in a WW2 B-something bomber, 17 or 24, I've not seen the flick)
Dawn Patrol (WW1)
Wings (WW1 aerial; received first-ever best picture Oscar, 1927)
I'm sure more lurk just below our active memories. They'll all come to the surface in their own time.