Sodium dichlor is easier; calcium hypochlorite is stronger.

The main difference is that calcium hypochlorite adds calcium to the water and raises pH, while sodium dichlor is stabilized (contains cyanuric acid) and has a lower pH.

Calcium hypo is cheaper per pound of available chlorine, but you have to pre-dissolve it in a bucket or it’ll bleach your liner or plaster. It also spikes your calcium hardness, which is fine if your water is soft, but bad if you already have hard water or a vinyl liner.

Sodium dichlor is more convenient—just toss it in the skimmer or broadcast it. But it comes with cyanuric acid (stabilizer), so if you use too much, your chlorine gets locked up and stops working. That’s the main downside: you can’t keep piling it on without checking your CYA level.

If your stabilizer is low, use dichlor. If it’s already high, use calcium hypo. If you’re just shocking once in a while, either works—just watch your calcium and CYA.