ah'd git me a ten guage double barrel shawtgun an' blast 'em wid both barrels if'n they invaded mah house. better judged bah six then carried bah twelve anyhoo. (transversed six and twelve deliberate

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Now that I got a little bit ofthe testosterone out of my posting, I'd have to suggest a fixed blade for sure, preferrably something about a foot and a half in length. (for my home anyways) basically something long enough to keep someone back, and short enough to use effectively in a hallway, small room, etc. My choice in length also has to due with power and speed potential of the weapon.
First choice would be a bowie. some suggestions being an Ontario Hells Belle, Mineral Mountain Hatchet works Bowies, and a Cold Steel Trailmaster or Laredo. I believe bowie knives inherently have a tremendous potential for protection, but they do require a bit more knowledge, practice and training than most other weapons.
Second choice would be a Himalayan Imports Khukuri, in the 18 inch range. There's a huge selection of 'em. I currently have an 18 inch Sirupati myself for similar duties, and my 17 inch Chiruwa Ang Khola aint bad either. The Ghurkas didn't become feared for thier tickle attacks ya' know....
Third choice would be a BK&T Machete. razor sharp, long, fast, and light. Pretty long list of celestially challenged folks that could probably attest to the machete's effectiveness if the celestially challenged could speak.
Fourth choice would be the tomahawk. Compact, hellaciously powerful and user friendly. Also offers alot of range variations from grabbing it right by the head if they're right on top of you to the end of the handle for a more powerful swing.
Sounds like legality and such could be a concern to consider too. so there is the subcategory of hatchets, rigging axes, framing hammers, etc.
Truth is that it's all gonna boil down to user preferrence and training. Competence is ultimately gonna play a much larger roll than the tool itself.
Hell, I wouldn't wanna get bonked, impaled, slashed,chopped,sliced, eviscerated,blasted, broken or ventilated by any of the items listed in this thread.