I own a piston AR and a DI AR. They are both accurate and in thousands of rounds fired through each rifle I have had no failures of any kind out of either one. That said I believe that of the 2 in an emergency I would grab the DI AR.
I am prejudiced in favor of the DI AR for the following reasons: It has an almost 50 year service history. Everything that can go wrong with an AR is known. the wear patterns, necessary PMCS, component life etc. are all known. Any piston AR is by comparison a recent experiment.
Parts for the DI AR are everywhere, even in a SHTF of TEOTWAWKI proportions you can scavenge parts from many sources. Piston ARs all use proprietary parts that can only be sourced from the manufacturer.
I was trained on the DI AR in basic and over 10 years in National Guard service so I am very comfortable and familiar with field stripping and maintaining a DI AR.
High quality DI ARs are being made by more and more companies every day. I believe that you get more value for your money with an AR than with any other semi auto rifle for sale today.
As to what is good for < $ 1000? The answer is: PLENTY
You can put together a top tier DI AR from Bravo Company for around $ 850. or Spikes Tactical for around $ 750. One of slightly lesser pedigree but still a 100% GTG rifle can be had for about $ 615 from DSA and that price includes using A BCM bolt carrier group.
I have the details posted here
http://www.thehighroad.org/showthread.php?t=513883