Hello. tl;dr is new job may force me to leave Delta for better SEA to LHR direct times. Work pays for business class fights. Personal travel will likely be more on Alaska. Should I make BA or Alaska my "home" airline?

Details....
I’m based in Seattle (SEA) and travel a fair amount for work, primarily to San Francisco (SFO) and to France (NCE via Paris (CDG) or Amsterdam (AMS)).For the last 5-6 years, I’ve used Delta and am currently Delta 360.It looks like I’m taking a role with a company based in London that will have me making the SEA-LHR flight twice a month.

BA has a Sunday SEA departure direct to LHR that arrives Monday at 7am. This is great for arriving for morning work on Mondays. Unfortunately the Delta and Virgin SEA-LHR flights don’t arrive in London until 9:45am.

I hate to leave Delta and am exploring options to stay but I may have to switch to BA and Oneworld. Having Alaska Airlines on Oneworld makes it attractive for a Seattle resident.

My question is, given that I will be traveling regularly for work on the SEA-LHR route flown by BA but living in Seattle and likely using more points for trips on Alaska Airlines. Which company should I choose as my home airline? Work trips from SEA-LHR will be business class and paid for by work.

Thanks in advance for advice. Apologies if I’ve left relevant information out. Happy to add details. Below is the information requested at the beginning of this thread.

I'm a very frequent flyer but not an expert on the intricacies of these programs so I apologize if something I'm asking is obvious or could have been easily found somewhere else. Any links for additional reading would be appreciated.


(1) What is your home airport?SEA
(2) What types of fares do you usually buy ?on Delta work provide coach for domestic and Delta One for transcontinental or international (which I did 7-9 timers a year)
(3) How many miles do you usually fly each year? 150-200K
(4) Do you have any kind of status at present? What is it? Delta Diamond / 360
(5) What is most important to you in a FFP? Frequent upgrades, lounge access and points to use for personal travel. Upgrades for personal travel would be great as most work travel will be paid for as international business class in this new situation.
(6) Which routes do you fly most often SEA to LHR
(7) Preferred Airlines – see above. Prefer to stay on Delta but early arriving flight at LHR may force change for new job
(8) Do you travel for work or pleasure? I travel most for work. Business class.