Smaller is better, or to be more specific, a slightly shorter reach/ETT compared to your road sizing is common. Some companies already incorporate this into the geometry so check the charts to compare. Some cyclocross racers like to be fit the same as their road bikes, but the majority have a slightly more upright position, probably due to the rigors of racing and the strain it puts on your back etc. Also realize that the position should be optimized for the hoods where you will spend the majority of your time. If you want to match the fit to your road bike during training season that is much easier on a slightly smaller bike than a larger bike too.