Was the Pit seriously "attacking" your dog, was it just trying to play - but too roughly? If it was the former, I'd do whatever it takes to get it fenced in, muzzled, whatever. I'd be paranoid to ever let my dogs outside when the vicious dog next door can literally run into your yard and rip into them. I wouldn't even have wasted my time coming onto this forum to ask if I should do anything about it.
I'm guessing you wouldn't either, so I'm also guessing it was the latter. The pit was just trying to play, but got too rough. In that case, I'd personally probably do the "anonymous tip" thing. The issue is certain to be dealt with, and you avoid any antagonism with the neighbors. Who knows, if you try to confront them yourself, they might just assure you it won't happen again.
I'm guessing you wouldn't either, so I'm also guessing it was the latter. The pit was just trying to play, but got too rough. In that case, I'd personally probably do the "anonymous tip" thing. The issue is certain to be dealt with, and you avoid any antagonism with the neighbors. Who knows, if you try to confront them yourself, they might just assure you it won't happen again.