Brian Kelly knows travel loyalty programs. Kelly provides advice on leveraging loyalty programs on his site, ThePointsGuy.com, and keeps subscribers notified of loyalty promotions.

Gone, it seems, are the days of simple points-for-travel-miles programs. Now, says Kelly, revenue is the focus.

“For much of frequent flyer programs' history, travelers have earned miles based on the distance flown. Now, more and more programs are switching to revenue-based programs, meaning you'll earn miles based on how much money you spend. For budget economy travelers, this is generally bad news. But for those who pay full fare or travel in premium classes, it's good news.”

Kelly firmly believes that a loyalty program needs to offer its loyal customers something that will make them continue to fly.

“For most, that means upgrades. Comfort is key when flying a lot, so if you're rewarded with complimentary upgrades, that makes it much more appealing. There are many aspects to a loyalty program, but I generally find upgrades to the in-flight experience to be one of the most important benefits.”

Kelly says there are three main factors to consider when comparing loyalty programs. 

1. In-flight perks

If you're going to be investing a lot of in-air time (and money) with an airline, you should expect to get a lot out of it. When looking at the elite status levels, make sure the program is rewarding you — whether it's upgrades, preferred seats, free drinks, snacks and more.

2. Fee waivers

Those pesky fees can add up. Especially if you're a traveler who needs flexibility, a great loyalty program will reward you by waiving things that could cost in the triple digits for non-elite passengers.

3. Bonuses

With the exception of earning elite status, at the end of the day, it's all about earning those coveted redeemable miles. Look for a loyalty program that awards elites with bonus incentives for flights.