I personally shoot for humidity between 45-55% for the first 18 days and increase it to about 65-70% for hatch (usually 65% but some breeds, like Marans, I go a tad higher). I will alter the humidity if I feel like the air cells are growing too fast or slow in early incubation for my incubators in my area, those percentages seem to work very well.
I do think there are a lot of factors that will change what humidity works best for everyone and that's why it's all across the board what everyone says works for them. What incubator you're using, where you keep the incubator, what your weather is like, all of these things can make a difference.