Delta is offering the highest welcome bonus we've ever seen on all 3 of its main credit cards, making now the right time to open one

Read on to learn more about the three cards, and see which one is best for you.

Best for the casual Delta flyer: The Gold Delta SkyMiles® Credit Card from American Express

Welcome offer: 60,000 Delta SkyMiles when you spend $2,000 in the first three months. Plus, get a $50 statement credit when you make any Delta purchase in the first three months.

Small business version: Gold Delta SkyMiles® Business Credit Card from American Express (70,000 SkyMiles after spending $4,000 in the first three months. Plus, get a $100 statement credit when you make any Delta purchase in the first three months).

The Gold Delta SkyMiles card is the best of the three for the casual Delta flyer, someone who finds themself on the airline a couple of times a year, but doesn't fly regularly enough to use the heftier cards' perks (more on that later).

One of the biggest perks: The card offers a free first checked bag for the cardholder and up to eight people on the same reservation. Delta charges $30 each way for a checked bag, so this can save up to $60 per person on a round-trip itinerary.

Cardholders and travel companions also get Zone 1 priority boarding. This means you can board the plane sooner, giving you plenty of time to settle into your seat or find overhead space for any carry-on luggage. Zone 1 is after most Delta elite frequent flyers and extra-legroom passengers, but is usually within the first half of passengers to board.

Other perks include discounted day passes to Delta Sky Club airport lounges- $29 per day pass - as well as a 20% discount on in-flight purchases (in the form of a statement credit), such as food or drinks, and no foreign transaction fees.

Like the other Delta cards, the Gold SkyMiles card earns 2x Delta SkyMiles on eligible Delta purchases, and 1x mile on everything else.

The Gold Delta card has an annual fee of $95, which is waived the first year. This is a great value considering the perks, not to mention the welcome bonus - 60,000 SkyMiles is more than enough for two round-trip flights across the United States, and is just shy of enough for a round-trip to Europe. The card normally offers 30,000 SkyMiles.

Best for more regular flyers: The Platinum Delta SkyMiles® Credit Card from American Express

Welcome offer: 75,000 Delta SkyMiles and 5,000 Medallion Qualification Miles (MQMs) when you spend $3,000 in the first three months. Plus, get a $100 statement credit when you make any Delta purchase in the first three months.

Small business version: Platinum Delta SkyMiles® Business Credit Card from American Express (80,000 SkyMiles and 5,000 MQMs after spending $6,000 in the first three months. Plus, get a $100 statement credit when you make any Delta purchase in the first three months).

If you fly somewhat regularly, the Platinum Delta SkyMiles card is a better option, thanks to an often-overlooked benefit that can completely cover the $195 annual fee each year.

The Platinum Delta card has most of the same perks as the Gold version, like priority boarding, free checked bags, 2x SkyMiles on Delta purchases and discounted Sky Club access.

However, the Platinum Delta comes with a huge perk - it's so useful that I'm planning on keeping my card indefinitely.

After your first year with the card, you'll get an annual domestic companion pass each year at your card-member anniversary. A Delta companion pass is essentially a buy-one-get-one-free coupon. When you book an economy-class flight for yourself anywhere within the continental US, you can get a second ticket for free, other than minimal taxes and fees.

The companion pass completely blows away the annual fee for me, which is $195 and isn't waived the first year. My wife and I fly domestically at least a few times a year, whether it's to visit family or friends, or to go on vacation. So I save my companion pass until we're taking a flight together that costs more than $195 each. You can read more about the Delta companion pass benefit here.

While you don't get a companion pass the first year, the 75,000 SkyMiles from the welcome offer more than outweigh the annual fee - that's enough to fly from the US to just about anywhere in Europe round-trip.

The MQMs in the welcome bonus can be a boost for anyone looking to earn or keep Delta Medallion frequent-flyer status. Plus, each year that you spend $25,000 or more on the card, you earn a bonus 10,000 SkyMiles, 10,000 MQMs, and have the Medallion Qualifying Dollar (MQD) requirement for most elite status levels waived.

When you have Medallion status, you can enjoy things like free upgrades to first class or extra-legroom seats whenever you fly, subject to availability.

Best for Delta Medallion frequent flyers: The Delta Reserve® Credit Card from American Express

Welcome offer: 75,000 Delta SkyMiles and 5,000 Medallion Qualification Miles (MQMs) when you spend $5,000 in the first three months.

Small business version: Delta Reserve for Business Credit Card (80,000 SkyMiles and 5,000 MQMs after spending $6,000 in the first three months).

The Delta Reserve card has a higher, $450 annual fee, but it has a few additional perks that can make it worthwhile for some frequent flyers.

Like the Platinum SkyMiles card, it offers a domestic companion pass. However, that pass can be used for first-class tickets, not just economy.

Additionally, the Delta Reserve offers full access to Delta Sky Club airport lounges whenever the cardholder is flying with Delta (the Gold and Platinum SkyMiles cards offer discounts on single-access Sky Club passes).

The Reserve has one other major perk, which can be crucial for travelers who hold Delta Medallion elite status.

Delta Medallion members are eligible for complimentary, space-available upgrades to first class and Delta One on flights within the US and the region, including Mexico and Central America, and extra-legroom seats on international flights.

Upgrades clear in hierarchical order based on a number of factors, including each passenger's Medallion status level, the original fare class they booked, and a few other factors. The first tiebreaker for people with the same Medallion level and fare class: whether they hold the Delta Reserve card. Reserve cardholders will be prioritized over those without it. If there's only one seat left and two members are still tied and both have the Reserve, it continues down the list of tiebreakers.

For travelers who fly a lot and frequently find themselves one or two upgrade-list spots away from getting that first-class seat, holding the Reserve can be extremely valuable.

$95 annual fee: Click here to learn more about the Gold Delta SkyMiles Credit Card from American Express from Insider Picks' partner: The Points Guy.

$195 annual fee: Click here to learn more about the Platinum Delta SkyMiles Credit Card from American Express from Insider Picks' partner: The Points Guy

$450 annual fee: Click here to learn more about the Delta Reserve Credit Card from American Express from Insider Picks' partner: The Points Guy