I'm not au fait with how things are at EF, but I'll proffer some thoughts on BA as an option for someone in your position. Ultimately, if you see it as somewhere you'd like to end up in the long run then it would be sensible to get on the list as soon as possible. That will give you the most options in terms of being able to pick, in a few years, between day trips from LGW, tours from LHR, beers on the beech and nights out of bed on a LH fleet, or going after a SH command at the earliest opportunity. In that vein its probably worth thinking about where in the UK you want to live, how far that is from the respective bases and whether that might change in the future.
From your comments, you seem to value the "vibe" you sensed at the Norse interview. There isn't a whole lot of "vibe" at BA. You, and only you, will be responsible for garnering the satisfaction you take from your worklife. While the small base of LGW might offer some sense of community (as it certainly used to pre EF) it is a largely anonymous place. No one will take any interest in motivating, inspiring or leading you, or even what you do - unless you do something wrong, in which case every interaction between you and the company will be recorded and examined. You will not have any sort or working relationship with your so called manager. Some thrive in this autonomous environment.
Things you haven't mentioned that might influence my decision if I were a mid 20's single person - Staff travel. How do you plan to spend your leave? If being able to get yourself to places like CPT, GIG, YVR, SIN or SYD for not very much money and stand a fighting chance of getting on the plane are of interest to you, then its a valuable perk.
Other things that you might not be considering right now but that you might wish you had - Pension contributions on offer. Its boring, but its important. At BA you can put in up to 6% and BA will pay 15%. I've no idea how this compares to others. The other elephant in the room is loss of income protection. Some of us think it will never happen to us - but for some it does. Again I don't know about other airlines but it really should feature in the comparison.