For a long time all I could afford was one gun, and it was a 12 gauge Winchester 1200 pump shotgun. The last I heard it still is the most powerful small arm in the world. And its efficacy is waaay under-rated.
If portability is necessary then a Glock 19.
"Socialized Medicine is the Keystone to the Arch of the Socialist State.” -Vladimir Lenin
"I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them." - Thomas Jefferson (An early warning to Obama care)