This will make me vilified by Ninja Gaiden fans, but I like Ninja Gaiden 3: Razor's Edge a lot more than Ninja Gaiden Black nowadays. Ninja Gaiden Black has terrible level design, terrible camera, terrible characters, terrible story, meh boss fights, still looks great, plays great besides bland enemy variety.
Razor's Edge is a lot faster combat wise, camera doesn't suck nearly as much, has fun setpieces that help pacing a lot, simple level design, serviceable characters and story, great boss fights, more varied enemy variety.
Haven't played NG2 in a long time, can't say where I'd rank it now, probably well above Ninja Gaiden Black. NGB's level design is so bad.