Loin is the best choice. Pork should be cut into matchstick-sized pieces. It will slice easily if you first freeze the meat for at least a half an hour. Daikon is a variety of radish. It looks like a big white carrot, but tastes peppery like a radish.
Daikon have a lot of moisture, so after cutting, squeeze out extra liquid by pressing in a colander.
This keeps the egg roll from getting soggy. If you can't find any daikon, substitute jicama or red radish. Daikon radish and carrots are first peeled, then sliced into very thin layers using a vegetable peeler. Slice across the layers to make toothpick-sized pieces. Leaves are thinner, crisper, and milder than common green cabbage.