I have the .41 Mag and I like the heck out of it. I shoot my Ruger Black Hawk every weekend. I hand load with 210 grain home cast lead semi wad cutters. They drive tacks.
If you do not hand load do your self a huge favor get the .44 mag. You can find ammo for it at WalMart. If you get the .41 Mag it is harder to find ammo for, and most times it will cost more as well.
Both will do the job. Get the one that is more practical for you.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.