As writers, whether in the self publishing industry or not, we frequently come across both spelling and grammatical quandaries. Do you spell program as program or as programme? If you describe an event from history, do you describe it as a historic event or as an historic event? Moreover, does it actually matter which way you do it? Is there a right and wrong way, or is it all just down to individual taste or personal choice?
Taking the historic problem as the example, this of course comes from a fairly famous grammatical rule which you will, as a writer, certainly already be well aware of - that we should use "an" before words that start with a vowel- an eagle, an ambulance, an American, and so forth and so on. With words that do not start with a vowel, we always use just a - as in, a book, a wing, a whiny American, and so forth.
Things get slightly more confusing when it comes to word starting with "h". This is because of the sound of those words as spoken as opposed to the spelling of the words makes it seem as though they begin with a vowel - the sentence may read like "he was an honourable man" but it sounds like "he was an onourable man", which is why we tend to use the an instead of the a. That said, while this is definitely the most accepted way of doing things, a not insignificant minority will use "a honourable man", believing that the sound is overridden by the spelling.
p.s. The choice belongs to you... or a honourable editor.