OP, the Lyman is likely the most useful but things change over time, especially powders.
If you purchase your powders one pound at a time, you will need current manuals.
Online is OK but it's a pain in the butt. A hard copy manual is much easier to compare loads, especially at the bench.
If you reload specialty bullets, such as Nosler/Barnes, you may want to get one of their manuals or go online download/print their information.
If you have older powders on hand, such as H450 or HS6, you will need to go all the way back to the Lyman #45 manual to find load formulas.
There is one other thing as well, if you load obscure cartridges, then the Hornady manuals get the nod.
Some folks live on their Ipods or cell phones. No, I'm not being negative, having that much information at your fingertips is wonderful. I'm just not as comfortable with these devices as I could be.