I've used juice and cider, have had good results with both. If I'm buying juice I look for the stuff that's 100% apple juice with asorbic acid, cider I try and buy the ones that are just flash pasturized. End product is close to the same from what I've made. I have found that the juice batches do clear quicker than the ones made from cider and are ready to drink sooner.
Juice is filtered much better than cider and has asorbic acid added. Cider is pressed and filtered, but not as fine and still has sediment and pulp.
Some believe that good hard apple cider must start from cider. I've used both and don't think one is any better than the other. I've even used the frozen concentrate that's 100% juice, that works pretty well also.