Depends what you intend to hunt with your 223. For varmints such as gophers, prairie dogs, crows, etc, variable to 20X would be minimum IMO. If your quarry is larger critters such as coyote then 12-15X will be fine but I would still lean toward the higher magnification.
I have 2 Leupold 6.5-20X LR scopes, one on my 222, the other on a 22-250 and love them. The side focus is a nice option and IMO Leupold gives the best bang for your money if your budget can handle the price tag. I own 7 and have never had any issues to date.