Both my grandfathers served in WW2, one in the Army in France (great stories and memorabilia*), the other in the Navy in the South Pacific (don't think he saw much combat, that I know of). So for family connections, they kind of cancel out. Except for that I was much closer to my grandpa who was Army.
Then there's my lifelong LSU fandom, the Ole War Skule and its historic connections to the army.
Not sure if any of that is why I tend to pull for Army, or if it's just that Navy has had the upper hand for most of the time I've paid any attention, and I tend to root for upsets.
* one of my favorite possessions is my grandpa's old army helmet. It has a dent in it where a German soldier hit him in the head with the butt of his rifle, somewhere in France. My grandpa was a medic and was tending to another soldier when he was whacked, didn't see the guy coming. The blow rolled him over on his back, whereupon the German soldier was able to see my grandpa's sleeve patch indicating he was a medic, and the German soldier let him be. That's the story according to my grandpa, as best as I can remember it. That helmet's dent always gave me chills when I was a little boy......there's something haunting there, in the idea that Pe-Paw could've been wiped out and my whole family would never have existed.