Once in BA, with the exception of leave, EVERYTHING is dependant upon seniority; When you get you days off, where you fly, how soon you can change aircraft, what type you change to, when you get your command, the list goes on....
Though vaguely aware of this beforehand, now that I'm in I cannot stress it enough. I appreciate most of us probably all have a bit of inner caveman about flying the biggest/fastest jet etc on joining but don't let this short-term appeal dimish the quality/choices you'll have over an entire career.
TAKE WHICHEVER COURSE GIVES YOU THE EARLIEST START DATE!!
I nearly forgot, well done too!