What's your intended use?
1:7 will shoot just about every available load in 5.56/.223 pretty well, including all the heavy stuff. 1:9 will excel with lighter (~55gr) loads, and will not generally shoot anything heavier very well.
Non-chromed barrels tend to be more accurate, but less shit-resistant. A chrome-lined barrel will be slightly less accurate (how much depends on the quality of the chrome lining), but more weather/corrosion resistant on the inside.