The most popular way to do tapestry crochet is with the single crochet stitch, inserting the hook into the back loop or under both loops while carrying the other color(s). Each method produces a different result, with it’s own advantages and disadvantages. The choice is yours.
The same hook, thread, tension, and instructions were followed to tapestry crochet these baskets, inserting the hook under the back loop (left) or under both loops (right).
I think both are awesome. My thought would be if you are making something for yourself and wanted a more even scene you could do the both loops. But to make an original Mochilla bag then you would do the one on the right.