Online options are great, but not always inclusive. The Hodgdon website is free, and it is fantastic for their powders. You can't ask for much better.
Another online option is the Alliant website, but it's not as good, and it's getting worse. Every year they dump out more and more data for seemingly no reason, and never seem to test anything new except very, very rarely. Honestly most of the time I look in the 2000 Alliant manual since it's all the same as today, plus includes a ton of things you don't see in the 2024 website. Unfortunately they are obviously trying to push their newer powders hard to sell them. It's so bad now there are people that honestly have no idea how much data for Herco there used to be, and now all Alliant pushes is Sport Pistol and BE-86 which I never see anywhere. Sorry for the rant, it just sucks what Alliant has done as a company. Look up their 2000 manual online, it is a good one.
One often overlooked online option is the Nosler website. They don't have every caliber, but they have quite a few, and their data is solid. It is some of the closest data velocity wise that I have found for multiple calibers.
When it comes to books, the Lyman manual is one of the better ones for sure. I have the 50th, as well as some older ones. I have not bought the newest 51st. These are worth buying for sure.
Despite the criticism, the thing I go to first before anything online, or any other book is the Lee 2nd edition manual. Yes, it is copied data, which is great. It has data for ALL the powders in one place. It has a million calibers, and it's organized in a logical order which I love.
I did have the Hornady 10th edition manual. This is the one manual I would say to avoid. I'm a big Hornady fan, but they got hit by lawyers hard or something. It is embarrassing how weak most of the "max loads" are in that manual. You can look at 3 other sources, Lyman, Hodgdon, Nosler, and the will be very close together, say 44 gr max plus or minus .5 grains. Hell, you can put it in Quickloads and be right there too. Then there is Hornady telling you 38.2 grains is a max for the same bullet weight. I'm not buying the nonsense that it's their own bullets, or different brass, or whatever. To make matters worse, it isn't always the case. Sometimes their data is spot on, so you never know if the max load is going to be stinking hot, or pathetic. To top it all off the thing is organized by velocity in 50 fps increments. It's super annoying. This manual is basically useless without a second manual to verify it.