Why do you want to accumulate miles? You could get a cash back cc and buy the tickets you want with the cash you save.
You can get a credit card that allows you to "buy" tickets on any airline.
You can get a credit card that gives you miles on a particular airline.

I've chosen to stick with one airline and get status on that airline. I get free baggage, early boarding (great if you have carry-ons), and "preferred seats." That means you have to stay with one airline (or alliance). Occasionally I get upgrades.

My sister and BIL don't fly a lot, not enough to make elite. They have a cc that lets them buy tickets on the cheapest airline. Because my BIL puts all his business expenses on that, they have plenty of points to fly to Europe once a year.

What is best for one person may not make sense for another.