I'm probably an outlier in this, but for me, it's 9mm. My dislike for it admittedly has nothing to do with performance, but rather stems from when I was an assembler at Dan Wesson. All of the other calibers we built went together no problem. The 9mms were finicky. Failures to feed, extraction problems, recoil springs that were either too strong or not strong enough. You name the issue, we probably saw it. We made sure they functioned flawlessly before they went out the door, but getting them there took more work than anything else we built. To this day, I refuse to own one. What cartridge(s) can't you guys bring yourself to like?