Whereas RTR part time is available pretty quickly, so if you have kids under 18 it's readily available.
The Aspirational Part Time at BA is either 1 month on, 1 off, or 2 on, 1 off. Is means large blocks of time off year round, so a great contract!
I am a 75% Part Time Long Haul SFO at BA (21 on, 7 off) and love it!
It's the standard BA advice, but here EVERYTHING is done on seniority, so get in at the earliest opportunity. If you are coming here, you are coming for a full career, so take the earliest offered course, rather than hold out for one you really want.