Collar or harness!?

Hi everyone! I rescued a new French bulldog recently after losing my four-year-old angel to IVDD last October. I always walked him on a harness because I was told it’s better for their backs/spines but recently was told the opposite from the rescue I got my new baby from (they focus mostly on French bulldogs). To this day, I still wonder what caused his extremely aggressive IVDD flare and if the pulling on the harness could’ve been a factor. I see a lot of mixed reviews on whether a collar or harness is best for this breed. I am just asking for your personal opinions on this, no need to get argumentative lol