A Lyman #48 as my standard against maybe a couple dozen others, back to and including a Lyman #43, 1964 edition, purchased new.
Sierra, Hornady, Speer, Hodgdon, Lee, NRA, Barnes, Nosler and a small stack of pamphlets from the various powder makers are on my shelves. Each is "different", they use different equipment afer all, but I've never found any one to be particularly more "conservative" across the board than others.
Some thoughts on what the load book makers do:
First, powder makers don't arbitrarily "change" powders and primers over time to deliberately be hotter or cooler as some folks say. When they do make new powders they offer them as different types, not a sneaky change in an old type, so that change over time idea is a web fable. Fact is, power and primers are organic chemistry and can't be replicated exactly from batch to batch but the makers try their best to keep todays 4895 the same as it was in 1950, etc. Each lot IS a little different but it's a very little. We may need to tweek a good shooting load but we won't blow anything up if we just keep any good load without a new work up.
Each testing program provides the very best data they can but OUR gear isn't the same as theirs. Nor do they use the same gear between them, that's why we see differences between the books. Different books give us different powders AND some perspective on acceptable pressure/charge ranges. Everyone should understand that NO RELOAD BOOK can be the absolute gospel truth for all firearms, for all ages, amen.
I don't think any of them deliberatly strive to be more or less conservative than the others. It's OUR responsiblity to do as they tell us and that is, "Start low and work up ONLY if there is no over-pressure indication." Done properly, that rule allows us to accomidate ANY changes in cases, power lot number, primer, bullet, seating depth/OAL and temperature. If we KaBooM, it's our fault not the book makers!