I have used both 44 mag and 45 Colt in the Blackhawks, I enjoyed shooting them both and handloading for both shooting targets, but in the field I enjoyed the 45 colt more, it was easier on the ears when not having ear protection. Since you handload you could load either caliber how you want, over the years I have settled on the 45 Colt for my favorite at just medium velocities and found the heavy cast bullets go through a lot of things without the high pressures. (a 44 mag will too!) I guess I'm thinking if I want to raise the pressure on the 45. Colt to 44 mag pressures, I might as well be using the 44 mag. I stopped experimenting with the high velocities in 45 Colt some years back, where I live 900 fps max with a 250/255 grain is all I need and it's quite nice to shoot. I shook a 45 Blackhawk loose years ago with experimenting a whole lot, took about 10 years, Ruger rebuilt it, (for FREE!) after that I decided to cool it. They do make revolvers out there that are made for the high pressures in 45 Colt, but I'm just commenting on the Blackhawks.
Since you handload, it doesn't much matter, just what caliber appeals to you, .429/430 bullets, or 452.