My advice would be to pick up a few cheap, low grade BA war books and judge for yourself how realistic they feel to you.
(I think everyone has their own personal metric they would use to determine such a thing.)
For example, personally, I feel like out of all the BA DC war titles, G.I. Combat is the least realistic, mostly because of the premise -- the ghost of Jeb Stuart advising a US tank crew during WWII.
Afte that, I'd probably go with OFF as the second less realistic. SSWS/ Unknown Soldier has an espionage vibe, which I think works well for most of the series. OAAW/Sgt. Rock is, frankly, all over the place. Some issues are quite realistic, while others are not.
Bob Kanigher was writing most of these books (and sometimes all of them) and he is definitely not Garth Ennis. (Although to compare them is really unfair to both writers, as they are/were working in different eras, etc.)
If you feel like casting a wider net, I heartily recommend the British BA war stuff. Alot of it is being reprinted these days in hardcover collections. The BA Brits were very adpet at writing exciting, historical war material that also managed to pack a real punch.
In terms of quality, try checking out Charley's War, followed by Darkie's Mob, Johnny Red and a series called Battle Classics (with intros by Garth Ennis,who talks about his debt to the 70s British war comics and how they inspired his writing.)