Just a note, there is Hodgdon Universal Clays which has a burning rate nearly identical to Alliant Unique, and there is Hodgdon Clays, which is a very fast powder in the Alliant Red Dot and Bullseye burning rate.
Sometimes people refer to Universal Clays as Universal, and sometimes even as Clays. It's important to check a load manual to make sure what they are casually referring to actually matches published loads.
As to Alliant Unique vs. Hercules Unique, I honestly haven't found much of a difference in regards to Alliant being cleaner burning. The key is to up the charge to the point that you get a good fire lit and it will burn clean. It really should be referred to as a medium burning rate powder in terms of handgun powders. If you want to back off the throttle and having something that will burn clean at lighter loads, look at a fast powder such as Bullseye, Red Dot etc.,
