Most of the people doing AP tend to say, use the RGB colour channels. Some go hard-core and sample different colour channels separately to give more definition in certain colour ranges, and if you were an expert, you also might want to turn on the visual histogram with each photo. More power to you, if you do.
For me, I am persuaded in part by the idea that shades of gray are not the same as shades of colour, and I would rather have RGB in the mix to make what I get in the image as close as possible to what I see with my eye in some respects. But I thought I would try and see if maybe it would do something on the white balance or other settings. The first is with RGB, the second is “luminance” aka B/W.
Hard to tell at the washed out levels, but I would tend to go with the first all the time. If you were into the DSLR or high-end webcams, you’d have a more nuanced view, no doubt, but RGB it is for me.