My Parisian friends will tell you that inversion is more "classy".
Choosing Between Intonation/Est-ce que/Inversion Question Forms?
2 Answers By Expert Tutors

Olivia M. answered 03/22/19
Experienced Tutor Specializing in French And English
Bonjour! What a great question! It definitely seems like you have the right idea when it comes to the formality of the three different types of questions. I will say that in one of my French classes, it was mentioned that "est-ce que" is actually more formal than inversion. Why, I can't say I remember but I remember that being mentioned because I, too, had always learned that inversion was more formal. I've been living in rural France for the past 6 months and I feel that I default to "est-ce que" more than anything. I've not really been corrected but when I hear native French speakers, it seems like they default to inversion or intonation if it is a casual chat between friends.
For your more specific examples, I can see why you would have been instructed to use inversion rather than intonation. Especially with your example of asking someone to move over a bit. Using intonation, if you think about it in English, would be like asking a complete stranger, "You could move over a bit?" I feel like asking in this way, the rudeness would be more prominent with an "eh?" at the end. Can you hear how that would sound? Not exactly polite.
You seem to have the right idea with your "Il est gentil?" example as well. In English, would we be more likely to ask, "He is nice?" or "Is he nice?" Most likely the second one, just because it sounds a little nicer and is just more natural. I think you friend was trying to help you adjust your usage in order that you speak more like a native, not because your usage was incorrect.
Really, you have the right idea when it comes to in which circumstances to use the different types of questions but I would say that native speakers use the inversion method much more than anything else. Thus, if you want to speak French more like a native, try making the inversion method come a little more naturally. I think I'll try to do the same!
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