No Quarter was actually recorded in D, but the tape machine was slowed down to make it C# (Jimmy Page Interview). In live (1937 MSG, 1975 London, 1975 Earl's Court, 1977 Seattle, and on TSRTS, etc.), they played it in D, as you can confirm on YouTube videos. You could still decide to learn it in C#, but knowing what they actually did in the studio and on the stages, I would personally learn it in D.