As far as I can tell, the Muramasa is faster and stronger, but it drains faster, too. That's why I quickly switch to the HF blade for that rock throwing part on the final boss, lol. I still suck ass Free Blade mode
Ugh, I had to do some finger gymnastics there. No matter what, I couldn't get a precise enough cut with the Right Stick.
I'd line it up, then release, but the slice would shift slightly before the cut came out and Raiden would get a faceful of debris.