The ban you refer to was the 1994 Assault Weapons Ban as part of a larger anti-crime measure.
It didn't ban the AR specifically, just certain features; ARs were still sold during that time, but without a flash suppressor, bayonet lug, or magazines that would hold more than 10 rounds. Some states still have AWBs on the books, but not many.
Is there a chance of it happening again? Sure. Anything can happen, but the legislative environment has changed in the last 17 years. Gun owners pay more attention, gun rights have been advancing and not retreating, legislators (except in some die-hard leftist areas) know that gun control is a losing proposition, and the FBI stats themselves show that the AWB accomplished nothing. The original one only passed (even in a time when gun control was easier to accomplish) thanks to a 10 year sunset provision. Supporters thought they could make it permanent. They failed. So yes, one could happen again, but it isn't all that likely to happen anytime soon (but stay vigilant).
Back then, yes, existing rifles and magazines were grandfathered. If you have one, you could keep it. You could even sell the "pre ban" rifles and magazines (mags that now sell for $10 were going for many times that during the ban). Generally, the chances of a confiscatory (turn 'em in or go to jail) ban are very small; the government is hesitant to pull something like that. More likely you'd see them added to the National Firearms Act as firearms requiring extensive background checks and tax stamps, but again, that isn't terribly likely in the current environment either.
As for good one, here's my standard recommendations (I'm not an AR noob, but opinions on this are like, well, you get the idea):
For range use, plinking, basic defense: Bushmaster, Rock River, maybe DPMS
Very high quality: Colt, Bravo Company, Noveske
Somewhere in between: S&W, Stag, Armalite, CMMG
Meh: Olympic
Run away: Vulcan/Hesse/Blackthorne (all the same company, the name changes regularly)
