These two things are not unrelated, though. If you were planning to pay for E+, or if you were planning to check a bag, UA gives a meaningful discount to its frequent travelers. And if you make 1K, and can use your PlusPoints, that's an even more meaningful discount.

I shop on price, but the competitor needs to be quite a bit cheaper in order to outweigh the benefits of free E+, a chance at a CPU, and credit toward requalification. I generally find myself back on UA anyway.

True, was thinking more along the lines of customer service / IRROPS though.

If the OP is able to share more about their typical travel patters, what kinds of fares they're usually buying, and if there are any routes they frequent routinely or at least more than others, this will help yield better suggestions. IMO simply moving from one city to another doesn't necessarily trigger the need to switch programs on its own.

I had no idea that this thread would get so many comments! ha. sorry.

I fly internationally a lot (or used to, and plan to again!) mostly for pleasure and nonprofit work - no consistent route. I also have the budget to not go cheapest, if I can spend a little more for comfort.

So Delta Diamond options of global upgrade certificates are really appealing, as the number one benefit.

Alaska with their OneWorld alliance might make sense to look into, too - I hadn't considered that.

Alaska??? Unless you are regularly going to destination Alaska flies out of SFO that is nearly as limited as Delta.

UA alone has 48% of the seats out of SFO (Alaska 12%/Delta 8%)

Totally agree with the above, Alaska has very limited service out of SFO even to Hawaii now. Unless you are a frequent flier to SEA don't waste your flight time here. Similar if not worse situation with Delta although again there are specific cities which Delta does serve fairly regularly out of SFO (ie. SLC, ATL). I am long time out of SFO and I tried a run as using AS a couple years back and had to come running back to UA. It seems to be a situation of UA being the necessary evil and the devil that I know. If you do a lot of international as you state you obviously could still hang with DL and just hub out of ATL/DTW as others stated above. I prefer to just fly direct out of SFO with UA or *A carriers, jmho.

I disagree. With AS now being part of oneworld, it opens up a few more options than DL. Delta/Skyteam options are:

Aeromexico - Mexico
Air France - Paris
Alitalia - probably never flying there again at this point
China Airlines - Taipei
China Eastern - Shanghai
Delta - all their hubs
KLM - Amsterdam
Korean Air - Seoul
Virgin Atlantic (not Skyteam but a Delta partner) - London

With oneworld a significant amount more options are opened up:

Aer Lingus (not in oneworld but partners with a number of the member airlines) - Dublin
Alaska - numerous west coast destinations, a few others across the country
AA - Hubs
BA - London
Cathay - Hong Kong
Iberia - Madrid (seasonally)
JAL - Tokyo
JetBlue (not a member but close partner of AA) - transcons plus a few other destinations
Level - Barcelona (if you must)
Qantas - Australia
Qatar - Doha

From SFO oneworld offers much greater global coverage on far better airlines (with a few exceptions) than Skyteam. The only thing I'd mention here is that if I were going to go with oneworld, I'd probably go AA over AS just because of that JetBlue partnership, assuming OP is going to be doing some transcon flying. In fact, for premium transcons AA/B6 offer coverage to more cities than even UA/*A from SFO.

It really comes down to where the OP thinks they will be traveling. As mentioned upthread, if hoping to be upgraded, UA is a terrible option from SFO given the excessive amounts of both elites and paid J/F traffic.

If as the OP stated he is mostly flying now international then no question you have more than a point. However, AS and DL, have limited domestic service out of SFO at least for the majority of the destinations I fly. I use to fly virtually ever week to SEA, and sure AS was fine for that. Now I am in and out of the Hawaii and the throughout mostly the western US for work and AS no longer works for me out of SFO (at least the majority of the time). Don't get me wrong I wish I could fly AS or DL more, and I would love to use OneWorld but for now my international travel is way down and not entirely due to Covid but changes in work coverage. You comment about UA upgrades is right on as well, I have posted about that issue many times here. Even as a GS pax upgrades were tough out of SFO.

How much flexibility do you have when you travel? Can you fly midweek?

If you're limited to a particular flight on a particular day -- especially when it's Friday through Monday -- you may be disappointed with PlusPoints. If you're willing to say "get me to Asia and I'll figure it out from there," and you can fly out on a Thursday and return on a Tuesday, or something, then PlusPoints can be very useful (although they've been tightening up inventory recently).

That said, IIRC, as a Delta Diamond you're limited to four one-way upgrade certs. A base-level 1K can get four upgrades from the deepest discount Y fare,,, or if they continue the current promotional setup they have in place with Skip the Waitlist, something like six upgrades from Premium Economy with a greater availability for immediate upgrade. So, you may find that 1K is still better than Delta Diamond from SFO. Certainly, from SFO, there are a lot more upgrade-eligible flights on UA than on DL.

If you combine AS with AA, and make OWE on either carrier, you then get F lounge access at places like HKG, one of the best status perks there is. I do wish AS had more options from SFO, they are IME a much more pleasant airline to fly than UA or DL (or AA, obviously), putting aside the absence of lie-flats, that is.