If BA is your only Oneworld account, I would personally credit there - particularly if you were booked in one of the higher earning fare buckets, which is quite possible for a last-minute reservation. Even if not, and you could earn more miles with say AA, I'd probably still do so to prevent a small amount of miles becoming stranded somewhere and effectively unusable.

Small numbers of BA miles can actually be used quite effectively compared to most other FFPs, particularly on short-haul Reward Flight Saver (RFS) redemptions, which start at 4k miles off-peak one-way in Y plus £35 (all in, taxes & YQ paid). To avoid going further off-topic, you'll find more details over at the BA forum.