Which airline makes it easiest to spend all those miles?

Road warriors are great at racking up frequent-flier points but often frustrated by barriers that make it difficult to swap those points for seats to desired destinations.

Blogs galore (reliable, but often sponsored by mileage-reward credit cards) offer strategies for sorting things out, but few have the number-crunching power of non-profit Consumer Reports, which analyzed 70 million passenger trips over the past two years for its just-published "Ultimate frequent-flyer guide" identifying the best reward-seat availability for the 25 most popular U.S. award routes on the five biggest airlines.

The survey used figures from the Department of Transportation ticket database and found that Southwest offered the most award tickets of any big airline: 11.9 million, or 11.5% of total passenger seats. Southwest also ranked as the airline that provided the highest percentage of award-seat availability on 72% of the 25 most popular U.S. award routes.

That's likely due to the fact that Southwest doesn't place a lot of restrictions on how passengers can use their miles. "Every seat is available as an award seat, even the last seat on the day before Thanksgiving," Jonathan Clarkson, director of Southwest's Rapid Rewards program, told Consumer Reports.

The magazine found that, among the five biggest carriers on all routes, JetBlue booked the lowest percentage of award seats: 892,000, or 4.5% of all trips it booked.

The airline told the magazine that improvements to its TrueBlue program, including a lifting of the rules on point expiration, should make it easier for passengers to get award redemptions.

A chart showing statistics on all 25 routes studied is available for download, along with a useful list of dos and don'ts and a refresher course on how to choose the best mileage programs.

Among the tips:

• Try booking award seats a few days before you want to fly

• Have an airline ticket agent help you find available award seats

• Take note of mileage-earning restrictions United and Delta put on their programs and shop around for less restrictive programs

• Never buy points

• Get a credit card that isn't tied to one particular airline

Harriet Baskas is a Seattle-based airports and aviation writer and USA TODAY Travel's "At the Airport" columnist. She occasionally contributes to Ben Mutzabaugh's Today in the Sky blog. Follow her at twitter.com/hbaskas.