Wow! You are acquiring some impressive knowledge. Those au gratin potatoes are indeed very similar to scalloped potates except the au gratin have lots of layered tasty cheese throughout where scalloped strictly speaking are without cheese. That's the only difference.
Yes, there are many varieties of white potatoes. I like the Dutch Creams but happy to use the spuds called "unwashed". Red spuds roasted are pretty special, too. Dutch creams are yellowy inside and very creamy. Apart from that, don't mind which ones I buy for whatever purpose really. I sometimes buy the red potato, just one, as they are usually quite large and one will make two or three serves for myself.
