Goblet of Fire is an interesting one to start with, as it's the tonal bridge between the two halves of the series. I started with the first book and was quite surprised that everything became so dark later on; I imagine that starting at Order of the Phoenix or later would make it quite disconcerting when you went back to the beginning and discovered relatively cheerful wish-fulfilment adventures set in a world constructed mainly of terrible puns. I suppose beginning with Goblet of Fire would prepare you quite well for both sides of the series.

That's very kind of you to say; thank you! You're definitely a Gryffindor, which is a trait you share with th_esaurus, my mother and a great many of my favourite female fictional characters, so you're in excellent company.