In general, probably the Lyman reloading manual that is now up to its 50th Edition. It covers lots of rounds, with lots of manufacture's bullets (including their own cast) with lots of different American and some European powders.
The Lee manual is OK, but a bit basic and seems to just be a compilation of loads of free sources of reloading data (aka those supplied by the powder and bullet manufacturers).
There are plenty of other manuals, but they are often just for one manufacture's bullets, such as: Barnes; Berger; H&N; Hornady; Nosler; RWS; Sierra; and Speer. These, for obvious reasons, tend to be Americentric with regards to powders. If you use bullets specific to one of those manufacture's, then go with one of them. Personally, I feel the Berger manual is made-up by using QuickLOAD, as many of the recipes, when punched into the program, result in the same or very similar figures. Far too similar for comfort and safety.
As with regards to 'American' powders I am, as no doubt many others are, aware that many are not actually American, but sourced from around the world then sold under American branding.
You then have all the free data, or paid for in their hard copy versions, so either webpage based, or PDF documents from, to name but a few: ADI (Thales Australia); Alliant; Accurate (Western Powders); Barnes; Hodgdon; Hornady; IMR (Hodgdon); LOVEX (EXPLOSIA a.s.) Norma; Nosler; Ramshot (Western Powders); Reload Swiss (Nitrochemie 'Wimmis' AG); Vectan (Noble Sport); Vihtavuori; Western Powders; Winchester (Hodgdon).
As Laurie has mentioned previously, many of these sources (hard and electronic) do not agree with each other, have data tailored to work safely in the oldest of guns chambered for certain cartridges, and many other quirks.
As to what you should get, well that depends on what you want, what you have and what you can get. I've got most of the above, either in hard or electronic copy if you want me to check something specific.
Once you’ve chosen a source you’ve then got the choice of where to start. As Catch-22 said, many start loads are way below 15% of the max charge. Personally, I start at around 10% below the max and work up, noting the ambient temperature when firing. The latter is important as many powders can be highly temperature sensitive, primarily at higher temperature, but also below. Though the latter is not something to worry too much about here in the UK.