Here's my $.02

IMHO the best way to determine what program to use is to look at a few basic needs:

-What airlines provide good service (frequency, destination, etc.) from your airport.
-What destinations do you typically fly to for your revenue flights.
-What destinations do you want to redeem your miles to get to.

My experience is that you will find 1, possibly 2, airlines that will meet all 3 needs reasonably well. Understanding that there are probably multiple airlines that meet 1 or 2 needs perfectly but not totally miss the mark for the 3rd need.

With respect to DL being trash, I think that you will find advocates and detractors for each airline. Just remember that these are individual opinions based up individual experiences and variations of the 3 basic needs.

IMHO it is best to achieve status (the higher the better) on the airline you fly most. This includes your revenue and award flights. This ensures that you receive the most perks that are available with your status.

Most of the very frequent fliers, those able to acheive high status on multiple airlines, usually max out their status miles on their preferred airline before flying others.

If you already have EQMs with an airline but you aren't able to fly them for the majority of your trips then the benefits of crediting partner flights to that program to earn status on that airline are almost unusable.