Some time ago, I had this argument with a respected colleague. In the end, I agreed to accept the fact that both spellings are considered acceptable. However, I harbor a grudge. Simply stated, if you need a tool to ply something you use pliers. So, to my way of thinking, those who fly or things that fly are fliers. Those who cry are criers. Data points that outly the norm are outliers, and one who pries is a prier, so two who pry would be priers. Which would be better than associating with someone with priors.
There are exceptions of course, like dryers and fryers, but it seems to me that certain words require certain pluralization. As in, one who tells lies is a liar, and someone who buys is a buyer. Wouldn’t someone who is more than sly be slier? Actually, this is another case where both spellings are acceptable.
I’m done. But, I do want to go on record as having said; “When I produce marketing collateral, you will be getting fliers from me.” If you want to argue, I’m up for that, always.