Textbook. In math and science, it was very helpful (for me) to write lots of notes in the margins, highlight or underline things, and circle things for later review. I think this works best with textbooks. It also happens to be easier, though that’s not the point; best isn’t necessarily easier.
Even if someday they make it as easy, or easier, with a tablet, I’d still prefer students use textbooks. Otherwise, they go full lazy on you and get the crazy notion that learning is just about sweeping their eyes carelessly across their iPads. I think students have to get the feel for what they doing with pencil and paper in hand. Lots of practice is the name of the game. At some point shortcuts shortchange students.
It is a lot like when they went to calculators for even simple math, to these new $100+ ones. I can buy that if the student is going into careers in the sciences where complicated math is a must.
Hubby taught electronics, computers, telecommunications 20 yrs in the Navy; Navy was a breeze. And 20 yrs in Jr College. The big thing he ran into were at the Jr. College, where A/B grade math grads out of HS, had to go through his remedial math course first they were that badly educated. As the Memphis City School system JUST handed out grades like candy. His foreign students did NOT need remedial math. And yes at this level you needed a complicated calculator. But not in grade school. Basics first by rote.
My daughter is in college all of her textbooks on her Kindle can be annotated right on the page she is reading and organized into notes that she can then format into a text file for study with a few keystrokes.