If I can only have a single knife then it's going to be a 6" blade. Originally I thought that either the S6/S6LE, Skinny Ash, or Hell Razor would be my choices. However, when considering door breaching a thicker knife would be important. That leaves the S6/S6LE for me. The ASH1 would work too though I would prefer one of the skinnier flavors like the SE/LE.