Quote from 377OHMS:
It doesn't meet the strict definintion of "assault rifle" but I have a Springfield M1A and like it. Its got a very simple firing mechanism and it shoots with a very flat trajectory. I can comfortably hit targets at a pretty respectable distance with standard iron sights and it has alot of power (.308 or 7.62x51mm).
The marines employed it with an auto receiver as the M-14 in Vietnam before it was replaced by the M-16. It was very reliable and the only real complaint in the field was that the ammunition was rather heavy to carry and the weapon is somewhat heavy as well.
I guess it is considered to be a "main battle rifle" but would be my choice of weapon in a SHTF scenario. With some modern optics it is a formidable weapon. Out here in California we are limited to 10-round magazines so I have vest to hold a large number of mags and Springfield sells mags at a deep discount at the time you purchase the rifle. A nice sling is almost a mandatory accessory for a rifle this heavy.
Of all of the rifles mentioned so far in this thread the M1A probably has the best utility for penetrating various materials, stopping vehicles and for long range work.