Which Symbol Should You Use?

This debate has been raging for a long time, how long I’m not sure, but I’m here to keep it going.
    What sign do you use to indicate speech? “ or ‘ ?
    Many new writers, myself included, tend to use “. We were taught in school that that was the sign to indicate dialogue. The other sign is an apostrophe and could be used to quote something within dialogue and little else.
    When I was learning to type and throughout my typing career I was taught to use “ for quotes and dialogue. “ was over the 2 and ‘ was over the 8 and both were simple straight quotes, none of this facing the letter it was attached to.
    Ah, but you be old and went to school a long time ago.
    Both facts are very true. BUT I asked my granddaughter (16) what sort of quote marks she was told to use in her English lessons in this day and age. After looking at me somewhat blankly she said “. So it’s not just the people who were taught in the days of board rubbers and ink monitors who think like me.
    It has become the Established Publishing standard these days to use a single quote (or an apostrophe) to denote dialogue. (By “Established Publishing” I mean the big boys.)  But when did this happen and why?
    I have trawled through old books I have and some use “ while others use ‘. I recently read an ebook version of The Hobbit, which, according to the notes had been taken from an early version. That had “ in yet, yet a printed copy I have of The Lord of the Rings has ‘.  So was this down to the publisher? And yet… I have The Moonstone by Wilkie Collins and Far From The Madding Crowd by Thomas Hardy both Guild Publishing editions, printed by the same printers and yet one uses “ and the other ‘. And one of the very first books I bought as an adult, “Islands In The Stream”  by Ernest Hemingway and published in 1970 uses ‘.
    Another weird thing I have noticed… I have a tablet with a touchscreen keyboard. Very clever. It automatically shows capital letters after you put in a full stop followed by a space. And with those capital letters it gives you an option of “. Once you have started your sentence it goes to an ‘. Sadly it doesn’t go back to “ until after you have put a space after the full stop. As “ is only used for speech and nothing else, this begs the question, why Microsoft think it is important but publishers don’t?
    Is this important? Does anyone care? Well, you do get the odd nose turned up when some people find the ‘wrong’ sort of quotes being used. As if punctuation marks are more important than the words. And yet many of the smaller publishing houses still use it.
    I think using double quotes makes the dialogue more noticeable. I’ve recently gone through a book with my editor’s hat on and found the story brilliant, the typing perfect (and that takes a lot of hard work, even with spell checkers) but sadly lots of speech marks missing. Now this particular author was using the ‘industry standard’ single ‘. I wondered if he would have missed so many when proof reading his work if he had used “ which stand out a little better.
    Me? I will stick to using old fashioned “ until I’m forced kicking and screaming into using the apostrophe for speech.
    Oh, and as an afterthought. I have a copy of “Eats, Shoots and Leaves” by Lynne Truss. Wonderful book on punctuation. It was published in 2003. And all the way through it the good lady uses “ both for speech and quotes. Maybe I should ask for her opinion?