Airline Southwest recently ditched the cherished perk of free checked luggage, causing uproar among its customers.

The policy was seen as a key differentiator between the Dallas-based airline and its competitors and means that now, all the major US airlines charge for checked luggage on domestic routes.

So, does anything separate them when it comes to luggage policies?

We raked over the often convoluted baggage rules and fees for the nine biggest American carriers and discovered that some are definitely more generous than others when it comes to leeway with luggage.

We name the two airlines to avoid if you don't want to pay for carry-on bags, the ones with especially confusing explanations around their rules and declare which carrier is No.1 overall for carry-on generosity.

American Airlines

In the cabin: One personal item and one carry-on for free.

Your personal item, like a purse or small handbag, must fit under the seat in front of you, says American Airlines. Dimensions should not exceed 18 x 14 x 8 inches, or 45 x 35 x 20cm.

The total size of your carry-on, including the handles and wheels, cannot exceed 22 x 14 x 9 inches, or 56 x 36 x 23cm.

Grand overhead bin total: 45 inches, or 114cm.

In the hold: For travel within/between the U.S, Puerto Rico, and U.S Virgin Islands, the first checked bag fee in economy is $40 ($35 if you pay online) and the second checked bag fee is $45.

For travel to/from Canada, the Caribbean, Mexico, Central America, and Guyana, the first checked bag fee is $35 and the second checked bag fee is $45.

First checked bag is free for eligible AAdvantage credit cardholders and those with enough status; various international destinations, not including the UK.

Delta Air Lines

In the cabin: One personal item and one carry-on for free. Your personal item must fit under the seat in front of you.

Carry-on bags for the overhead locker may not exceed 22 x 14 x 9 inches, or 56 x 35 x 23cm.

Grand overhead bin total: 45 inches, or 114cm.

In the hold: For travel on domestic flights within the U.S, first checked bag in economy is $35, second is $45.

First checked bag is free for passengers on various international flights, including to Northern Europe; Delta SkyMiles Medallion Members and select Delta SkyMiles American Express Card Members.

United Airlines

In the cabin: One carry-on bag and one personal item for free "on most flights".

Personal items must fit under the seat in front of you, so they must be 9 x 10 x 17 inches, or 22 x 25 x 43cm.

Carry-on items for overhead bins must be no bigger than 22 x 14 x 9 inches, or 56 x 35 x 23cm.

Grand overhead bin total: 45 inches, or 114cm.

In the hold: United has a "checked bag fee calculator", which reveals that the first checked bag in economy on a domestic flight costs $40 ($35 prepaid) and must not exceed 62 linear inches, or 157cm.

The first checked economy bag is free on many international flights, including to London, but a fee of $60 is charged on some routes.

Southwest Airlines

In the cabin: One bag and one personal item. The bag should be stowed in the overhead compartment, and the small personal item stowed under your seat.

Carry-on items for overhead bins must be no bigger than 24 x 16 x 10 inches, or 60 x 40 x 25cm.

Grand overhead bin total: 50 inches, or 127cm.

In the hold: First checked bag in economy is $35, a second checked bag costs $45. Checked bags must not exceed a linear length of 62 inches, or 157cm.

Alaska Airlines

In the cabin: You're allowed one carry-on bag plus one personal item with Alaska.

The carry-on bag size limit for flights on all aircraft types is 22 x 14 x 9 inches, or 56 x 35 x 23cm.

Grand overhead bin total: 45 inches, or 114cm.

In the hold: First checked bag in economy is $35, a second checked bag costs $45. Checked bags must not exceed a linear length of 62 inches, or 157cm.

Frontier Airlines

In the cabin: One personal item is included with your fare.

Carry-on luggage incurs a fee of between $59 and a hefty $99 depending on your departure date and destination. Passengers must use a fee checker on the airline's website to find out what they'll be charged.

Maximum size: 10 x 16 x 24 inches, or 25 x 40 x 60cm, including handles, wheels and straps.

Grand overhead bin total: 50 inches, or 127cm.

In the hold: Checked bags incur a fee depending on the departure date and destination (typically between $55 and $100) and must not exceed 62 linear inches, or 157cm.

Hawaiian Airlines

In the cabin: You're allowed one carry-on bag plus one personal item.

The carry-on bag size limit for flights on all aircraft types is 22 x 14 x 9 inches, or 56 x 36 x 23cm. And bags must not exceed 25 Ibs (11kg).

Grand overhead bin total: 45 inches, or 114cm.

In the hold: First checked bag is $30 if flying to a neighbor island, second bag is $40. If flying to North America, first checked bag is $40 and second is $45.

Checked bags are free on international flights, except to Australia and New Zealand.

Hold bags must not exceed a linear size of 62 inches (157cm).

JetBlue

In the cabin: Each economy customer is allowed one carry-on bag and one personal item for free.

Carry-on bags must not exceed 22 x 14 x 9 inches, or 55 x 35 x 22cm.

Grand overhead bin total: 45 inches, or 114cm. There is no weight limit.

In the hold: JetBlue's checked baggage rules are quite complicated, with passengers charged different fees depending on their fare type and when they book the baggage.

Within the U.S, the first checked bag is $35, the second $40. For transatlantic flights the fee is $60 for "Blue Basic" but included for seats in tiers above this.

Hold bags must not exceed a linear size of 62 inches (157cm).

Spirit Airlines

In the cabin: All passengers can bring one personal item, and carry-ons are free for three fare types, but those on the basic "Go travel" option will have to pay a fee of between $37 and $65 depending on whether they pay online, when checking in, or at the gate.

Carry-on bags must not exceed 22 x18 x10 inches, or 56 x 46 x 25cm.

Grand overhead bin total: 50 inches, or 127cm.

In the hold: Spirit charges for all checked bags, with prices starting from $31.

Checked bags must not exceed 80 inches or 203cm in linear size.

Verdict

Southwest Airlines offers the best overall carry-on allowance, allowing passengers to take 50 inches of overhead bin luggage onboard for free.

Frontier and Spirit are also generous with the carry-on size allowance, matching Southwest's 50 inches for overhead locker luggage, but they both charge basic fare passengers a fee.

It's more difficult to separate the airlines when it comes to checked luggage, though many will find the fee-checking tools being used on some websites, such as Frontier and United's, annoying.

Southwest garners extra points here for laying out its fees clearly in a table, while JetBlue, Hawaiian Airlines' and Spirit lose marks for less-than-clear baggage explanations.

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