Unique is the most recommended mostly because back in the day it was the only choice available.
There were other choices, but not many, and none as good as Unique. Just go through an older reloading manual, such as my Lyman 41st and there is a paucity of choices.
I tried others, most recently Universal, and Unique is still the best for accuracy at standard pressures. It does a great job in that big case.
But to get back to choices, we have so many powder choices that I am going to say, if you clump powders into classes, the primary differences are the blaring labels and anecdotal claims. Just think of how many decades shooters swore that W231 was better than HP38. I have a Ken Warner article on the 45 ACP where he praises W231 and "gives up on HP38" . Ken was very clever, he never published his round count nor his group size. His recommendations were probably based on three shot groups, and he grouped them as "accurate", "very accurate".
When someone shows me a target like this:
Or this:
this tells me that the shooter is a good shot. And that he has fired enough rounds to make me an excellent case that this load is accurate.It does not hurt when the same shooter has a better score than me, by lots.
(You have to shoot Bullseye Pistol to discover just how impossible it is!)
I am certain I could find similar with H110/W296. Reloaders claiming one was better than the other. And W231 is the same powder as HP38, and W296 is the same powder as H110! These powders are the same stuff in different containers! And yet names, reputations, money made claiming that one was better than the other.
We do not see any of the technical data that will differentiate powders. Such as pressure curves, pressure extremes, temperature sensitivity, time to peak pressure, pressure duration, pressure consistency, ignition source sensitivity. None of that, just blaring labels, blaring product roll outs somewhat less spectacular than a 4th of July fireworks show, but just as noisy. How many times have you read that a new powder was the end of history? Hundreds of times? Tens of times?