I'd look at it like this:

You don't fly enough to save miles fast enough for many awards tickets, particularly on airlines which expire each year. Delta doesn't, so that's the one case where I would factor in miles.

Call the miles worth a penny (for argument). Maybe they are worth more, but maybe you don't use them all. Delta gives you 5, so 5% rebate.

If Delta's price is within 5% of the cheapest, fly Delta, collect miles. You could apply this to any other airline you might want to collect miles on.

Otherwise, choose the cheapest. Use the money you save to go where you want.