As stated above, seniority is king in BA and should a DEP 744 slot be your goal do be aware that you'll be at the bottom for a VERY long time.
What I mean is, and some of the 2005 777-DEP's are finding this, you're joining a senior fleet with absolute bottom seniority meaning typically over time more senior short-haul co-pilots will be constantly bidding onto the 744 ahead of you. The current majority of new extrants serve 5 years (ish) on shorthaul before moving to longhaul but if you go longhaul from day 1 you'll be behind all those more senior copilots coming onto the 744 ahead of you from the last 5 years.
It's a warning but unlike being the SH fleets where you'll likely move upwards on your fleet seniority then move to LH, you'll be getting blindlnes (call that you'll be rostered with very little say) and will work a good number if not most weekends.
Don't get me wrong, you'll be in a great company flying a great aircraft with great guys....but you'll be junior for long time