I liked the Faber series the best of the adult piano books that I used. Finished them and am now in John Thompson’s grade 3. It is much more challenging. When I first started piano I did group lessons. The teachers changed twice after the first year and each teacher would change books each new semester. When I changed to private lessons the teacher used Faber which had a more logical progression of skills than some others and more gradual, so that it didn’t seem to be as much of a struggle.