I suppose there isn't any hard rule about powder co. vs bullet co. It depends on which company and how much you trust their data.

For example, I don't use Hogden data at all. Their data is quite safe, but very low. It wildly exaggerates the velocities you will get for a given charge. My favorite manual is Hornady, I believe their data more closely matches reality because they test in real guns.

Alliant uses Speer data, since they are the same company. I consider either is a good choice. Speer data seems to run a little warmer than Hornady for the cartridges I load (.38 and .45 auto), so I am a little hesitant to use Speer's max loads.

Lee is just a compilation of other's data, they don't do any load development or testing. It is sometimes a bit vague which bullets is for which data. I would rather get original data, not Lee's "intrepretation" of it.