Thanks. Is there a difference between DL, AA and UA in terms of a credit card that I could obtain and get lounge access starting with my first trip (even for a per-use fee) while I'm building status the first year? I'll be doing 4x per year for a 10 year commitment. Would a million miles get me any status with any of the three even though I'd never hit top-tier in any single year? I've got 200k lifetime with AA now. Nothing close to that on UA or DL.
As for what I value for the coach product, the only thing I really value is a realistic opportunity to get an upgraded coach seat with more leg room as a lower tier frequent flyer. Not anticipating business or first upgrades.
Getting 2nd tier status on DL, AA, or UA will give you access to lounges during international trips. If you're flying DSM-LAX-AMD regularly, that's almost 20K per round trip, so with 4 trips/year it seems like you'd have no problem with the 50K requirement for 2nd tier status and you'd also have enough for 75K third tier status, assuming you also have enough spend. What would you consider "best coach experience"? Access to seats with extra leg-room? Free/better in-flight entertainment? Free alcohol in coach+? Chance of upgrades? The big 3 are pretty similar for most things IMO, but there are subtle differences in these depending on what you value. Really, it probably makes the most sense to just go with whoever is the most convenient out of DSM for the bulk or your travel, and if it's a tie since you're flying within India regularly maybe also who has the best partnership with the airlines you fly there.
If you really want to go all-in on free lounge access, you could also look into crediting your miles to an international partner airline. Often if you get 2nd tier status with an international partner that gives you lounge access not only for international itineraries but also for domestic trips. Your chance of domestic upgrades doing this will be much less than if you credited with DL/AA/UA directly though and you might earn fewer redeemable miles depending on your spend and what fare classes you buy.