I have used both in a bunch of different calibers. I use Unique for lead SWC 44 mag loads. I have only used Auto Comp in pistol loads such as .40 S&W, 9mm, etc.
I will tell ya one thing about Auto Comp, it had to be the dirtiest powder I ever used. 100 rounds of .40 in my Sig P226, and the thing was caked with soot. I mean a 2 to 3 millimeter layer all over the nternals. I thought it was just me and my reloading habits. A couple of fellow reloaders also tried it and found it to be very dirty as well. It did shoot pretty well with very controlled recoil but was too dirty.
A nice alternative to Auto Comp is Alliant's Power Pistol. Shoots similar to Auto Comp, actually I thought PP was better but PP is much cleaner.
