For caliber, it's probably a tossup as far as effectiveness. A bad guy wouldn't isn't going to get shot with either of calibers and say "well, if he'd used the other one I'd stop right here, but since he took the other one I'll keep attacking."
Both cartridges are proven and very effective.
Ultimately, I'd go with the Ruger because I'd just trust it more due to the rock-solid reliability of Rugers. As an owner of a 2 3/4" speed six, I can speak from experience when I say it's a fantastic wheelgun. I did have a Taurus for a little while (model 85) and it was excellent, so I'm not getting into a brand-war. I don't knock Taurus, I just give an edge to Ruger.
In the end it would really boil down to which one I would get more practice with. .38spl is cheaper than .44spl, so I'd pick the Ruger just because I could put more lead downrange and become more proficient with my chosen SD gun.
The ability to practice would be the deciding factor for me rather than brand, or effectiveness of that caliber.