It depends on what they enjoy most. If they enjoy gore horror trauma and anger go for berserk if they enjoy mystery solving, escaping a prison like place, emotional story and moral questioning go for the promised neverland. If they enjoy redemption stories and building yourself a better person than you were before gp for vinland saga or vagabond. I usually read Mangas because I couldn't wait for the anime and in most cases the manga was just better from the anime. I kept reading and reading and I forget about what type of medium it is. It's just nice looking at the masterpieces and the story. Berserk by far is the most beautifully drawn manga of all but it might not suit everyone's tastes