From my local airport, Delta is by far the most convenient airline to fly. With daily flights to Salt Lake City, Detroit, Minneapolis, Atlanta, and New York City, it's possible to fly virtually anywhere in the country or world with a single stop (although our New York flight is to La Guardia, so a bus transfer is sometimes required).
Moreover, with an American Express Delta Platinum credit card it's easy to reach Silver Medallion status each year by manufacturing $50,000 in spend and earning 20,000 bonus Medallion Qualification Miles (and simultaneously dodging Medallion Qualification Dollar requirements).
Unfortunately, Delta gutted their redeemable mileage earning this year by linking it to the price of your purchased airfares.
Fortunately, Alaska has continued to allow Delta flights to be credited to Mileage Plan based on distance flown, at a lower rate for discount economy fares and a higher rate for first class fares.
I love checking bags
If you just read travel bloggers, you might get the impression that airlines only remain in business out of glee at losing checked bags. Sure, it happens sometimes, but I love being able to throw any old thing I think of into my biggest suitcase and pick it up at my destination.
And I especially love doing it for free, which Delta Silver Medallion status lets me do, for up to 9 people traveling on the same reservation.
On outbound flights free checked bags are easy
Even if you plan to actually fly on your Alaska Airlines Mileage Plan number, it's easy to take advantage of Delta Medallion status to check bags for free on your outbound flights: simply check in with your SkyMiles number on your reservation, then once the airline has possession of your bags change the frequent flyer number on your reservation to your Mileage Plan number (note that this is impossible if you've requested a Medallion Complimentary Upgrade).
On return flights it's slightly trickier
Once "travel has commenced," that is to say, once you've actually boarded any flight on a single Delta reservation, you can no longer change the frequent flyer number linked to your reservation.
What I discovered on my return flight from Salt Lake City after Christmas was that check-in agents are able to honor the free checked bags you receive for having a co-branded American Express credit card, even if you aren't flying under your SkyMiles account number.
To do this, after checking in on a Delta terminal, choose however many checked bags you wish, and when prompted for payment choose to "pay with cash." You can then show the baggage check agent your co-branded American Express card and ask them to honor the free checked bag.
I'm sure there are agents at some stations that are either unwilling or simply don't know how to waive checked bag fees for co-branded cardholders flying on non-SkyMiles frequent flyer numbers.
But I'll be using this technique whenever possible to check my bags for free when I find myself flying on Delta roundtrip itineraries.