I always check a few of them (Touring Plans, Undercover Tourist, WDW Prep School) and then compare and contrast assuming that I'll have good takeaways from each. Some are more detailed (which park which day) and some are more general, but I'm an over planner, and I really enjoy the research.
I can't be the only one who never bothers with a crowd calendar. I base my travel dates on other factors - when I can go, avoid very hot weather, avoid major holidays if possible.
They've all been inaccurate enough that I no longer bother, beyond very general trends. For example: October is busier than September, during Party season Party days in MK are uncrowded, but non-Party days are busy, etc.