Glock 19. I can hide it under any clothing and take it anywhere. I can wear it on my hip and climb through endless miles of rough terrain without handicap. I can put three rounds into each member of a 5 man crew in a sedan with good speed and precision. I can shoot a fully armored opponent through exposed areas at over 25 yards. I can score hits on a human target at 100 yards. I can hunt to survive with it better than anyone ever could with any bow and arrow. I can carry hundreds of rounds in a backpack. I can shoot a mature male grizzly bear right through it's skull and vertebrae and kill it instantly. I can find ammunition, magazines, and parts for it anywhere. I can shoot it over a hundred thousand times without ever needing the services of a gunsmith. I can obtain subsonic ammunition and get suppressed performance good enough to use in close proximity to human activity without detection. I do not need any other firearm and will not shed a tear if I have to leave the rest behind.