Well, with more fps you get smoother movements obviously. NTSC and PAL als norms don't have any meaning for today's presentation methods. If that setting is your vehicle to higher frame rates, go with NTSC. I live in Germany where PAL is the usual norm because we have 50 Hz power, but I'm still going with NTSC and 30 fps.
That said, the h.264 max bitrate that the Mavic encodes video with is fixed at 60 Mbps. If you use 24 fps, you get more bits per frame than at 30 fps. So in theory, if you have lots of detail in the image, there might be a difference in image quality per frame. Don't know if that really shows up in practice though.