Getting the manual from the manufacturer of the bullets you use most makes sense to me. Partly because that's the only way to have some confidence in suggested COAL.

I have Hornady and Lyman manuals. The "Service Rifle" section in Hornady's is unique and you need it if reloading for an M1 Garrand or M14/M1A variant. However, I wish Hornady listed pressure data like others do. Lyman manual seems useful mostly for lead bullets.