Hm, tough choice. A lot of you don't seem to be too gun-oriented, so you may want to do some research. Start with Home defense weapons.
Anyway, I'd want either an 12 gauge shotgun or an old bolt-action Rifle, like a Karabiner-Kurtz.
Shotguns are perfect for home defense because of their simplicity and firepower, and a 12 gauge can utilize many variants of buckshot, whereas a ten gauge packs heavy recoil, and a 16 or 20 gauge cannot use as much ammo types as a 12 gauge.
A Bolt-Action Rifle is an extremely reliable weapon. They are very easy to clean, but are also somewhat difficult to reload. On the upside, shell casings must be removed manually. This means you will not leave any evidence behind that could potentially thwart you.
If I could pick both, I would. However, I would have to go with the bolt-action.