We could debate the best books,,Arban, Saint Jacome, Schlossberg, Williams, Glantz, Hering. Probably any one of these would be all you need when you reach a certain level (no I never will be there..lol)
But the Clarke series: "Elementary Studies", "Characteristic Studies", "Technical Studies", and maybe the all around best for daily maintenance "Setting up Drills" are worth a second look.
I have so many books I could literally start at Arbans and go through them all just once and could not live long enough to finish.
I really do love though playing Arban with my oldest horns. You gotta wonder how well the best players of the day (1870's) managed with the quality of the valves/lubricant then.