Here's one that could go either way; I only wish the O.P. had provided more context:
He left the house ___ I was still sleeping.
Would this be better completed with when or with while?
Had the O.P. elaborated with something like this:
I don't really understand the rules for when I should use these two words. Which one should I use?
then I would probably suggest migration to ELL. However, had the O.P. provided this exposition instead:
I understand what the two words mean, and how neither one would present grammar issues – I'm just wondering if, given the choice to use either one, there might be some subtle rule that would make one of them the more preferred word in a particular context.
I wanted to call attention to this question because it illustrates how the same basic question could be a good fit for either site, and the appropriate location would depend on the depth of the O.P.'s underlying question, and the O.P.'s background knowledge.
In this case, I'm very impressed with Edwin Ashworth's answer to this question, given the location on which it was asked. Perhaps "Ask an ELU question, get an ELU answer" ought to become a mantra.