I got interested in rifles (and other firearms) after seeing the post-Katrina zoo in Louisiana on tv. Not that I'd plan on using it but better to have and not need than to need and not have, etc usual caveats and so forth, I was interested in reasonable price, high capacity if desired, and accurate enough out to about 100 yds or so. Milsurp rifles ended up filling that niche for me, stuff like the SKS, Mauser K98, Mosin M44, AK-clone. They're cheap and fun to collect, fun to plink with, quite reliable, and would be fine as a "neighborhood defender" if things got to a crazy Mad Max kind of situation. As I practice and learn more, these rifles are still probably capable of better accuracy than I am, and with some tweaking can probably be improved further.
So, reliability, ruggedness, simplicity, and price rank pretty high on my list. For the warding off looters thing the intimidation value of a military or military style rifle (say an AK or an AR, everyone recognizes them as Serious Medicine from tv) is pretty worthwhile too.