#3, as BA Club Europe is cramped, and the food doesn’t make up for it.

#1 has no First Wing at LHR, making for a less than premium experience in the over crowded Galleries, although a sufficiently long layover might allow the B Concourse Lounge for a better experience.

#2 is the same, but adds the chance for a nice UK261 payout when the A380 goes tech.

#3 is the sweet spot. Lieflat all the way, a simpler CBP experience than LAX or DFW, but PHL is not an outstanding facility. On the plus side, it’s a pretty simple location for the connection versus LHR’s secret gate system and DFW’s Terminal roulette.

#4 is decent, with some Lounges to hope between in T3, if you have time, but the lack of Emerald or a First ticket means no CX First for you. However, the final leg will feel like torture.

I flew BCN-LHR-LAX Nov 2024. Definitely take the short flight inside Europe then settle in with nothing else to worry about for the single longer Europe-US West Coast flight, vs two approximately equal length flights with an East Coast connection in between. (Not to mention, although my few US domestic trips in the past couple of years have actually been much less unpleasant than feared, I try to avoid US domestic at all after the pandemic years' misbehavior epidemic; not to mention that I find that US domestic airlines' booking practices makes Europe "low cost" look *good*, hard as that was for me to believe when I found it starting a few years ago - though of course a paid J itinerary should largely avoid that particular indignity).
Another reason to avoid the US connection is that, on AA at least, domestic F/ connecting from int'l J does not seem to get you lounge access, so your pass through PHL may be far less pleasant than you hope.

The relatively (or very) early morning departure out of BCN to get to LHR for the BCN-LHR-LAX routing is unfortunate, but the complaints about Club Europe (yes, narrowbody aircraft, yes, standard coach seats, with nobody in the centre seat) are overblown unless you're very tall, and the BA service tends to be decent. I also don't understand the complaints about BA J lounges at LHR; the dozen or so times I've used them in recent years (with the exception of one staff member who had to be convinced that, no, I wasn't going to download their app, and scan a QR code to book a shower - after a brief talk she personally walked me to the shower area and connected me with an attendant there) I've never found the lounges over-crowded or particularly disappointing. (That said, I also almost never travel at peak days/times, so I accept that there may be bad days).

Definitely the 777, not the 380, due to the BA still-old A380 seats (possibly have to step over someone's legs or vice-versa).
It is a shame that 787 service LHR-LAX doesn't seem to be an option, as there is a real difference in cabin pressure and air quality between the 777 (an aircraft for which I have almost as much nostalgia as I do for the dear, departed L1011 - I'm being serious, I love both the 777 and the L1011 as machines) and the 787, but I still came off the 11 hour LHR-LAX 777 flight in good shape.

Someone commented on Immigration/Customs at PHL vs LAX. I don't even remember my pass through LAX immigration/customs, so it must have been a non-event. I wouldn't choose one or the other airport for immigration/customs reasons; I'd definitely make the choice based on flight schedules and cabin experience.

And, totally, no, not three flights if reasonably avoidable, unless you're an "I WANT to risk a misconnection/ extra security grope/ greater chance for bag redirect/ etc" daredevil 😅.
I contemplated adding an extra leg just to get to fly on a 380 for an upcoming trip (it's the only thing in the sky that I've never flown!) but sanity ruled - never add an extra leg unnecessarily.

Have a good trip!

It is highly likely the LAX flight will depart from B or C concourse, so the B concourse lounge will be on the way.

There is a little-known website called wayfinding.maps.ba.com which, though intended to help the passenger step-by-step through the terminal, also tells you the gate long before the screens do.

Besides the tech. issues, the A380's old Club seats are actually preferred by some. For tall people, there is much more foot-room. And there are a few seats which do not have the step-over clash.

I don't believe this is correct. Int'l J is a qualifying flight, on the same day, and that is good enough for access.

I would choose option #2 just for the reason that I've never been on an A380, and they aren't going to be around much longer. The 78P will be around awhile still. But I like to hit as many types as I can.

The A380 is indeed an experience if you’ve never been on it, but my understanding is that BA is about to redo the A380 cabins with club suites etc., so they will likely be around for 10+ years.

Wait until the cabin refresh is done to do this.

Only thing I would add is if checking luggage connecting in PHL is a pain. Having to claim and drop it off. I'd probably do option #1 just for that, and I'd avoid the A380.

It’s a much better experience on airlines that don’t have 30-year-old seats in J.

(Ok, the seats aren’t that old, but the design is.)

You don't say when you are flying. If more than 3 months out I'd avoid PHL as the chances the 787 stays on a domestic route is reduced.

I for one don't like long then short flights. So I'd connect in LHR.