My last batch used a mix of plain apple juice and unfiltered farm cider. I find the cider lends the final product a cool, slightly caramel-like character that adds complexity without sourness; if you go whole-hog on it though you end up with cider that just tastes like farm cider that's turned a bit (note: still good). As far as blending commercial apple juices, I doubt you'll see much change, like PP said your best bet would be to juice/pulp some tart apples for that.
My ratio of starting materials is 2.5 gallons juice, 2 gallons farm cider, 6 tubes apple juice concentrate, Nottingham, and nutrient, if you're interested. No added sugar, the concentrate provides enough.