Not sure about the other 4, but I gotta include Operation Drumbeat in the top 5 just because it inspired me to play a Hardigan career in a Type IX.
...and it justified sinking a few merchies on the return voyages just using the deck gun.
I liked Torpedo Junction mainly cuz I live in Florida (near Jupiter Light) and it explained why there's still a lotta tar on our beaches... practically every page is an attack in that book, it's exciting but comes across a bit dry at times. I wouldn't put it in the top 5.