def. subversion...bombers & siege platform actually do useful things. Subversion usually ends up getting used on a planet you are about to glass, which kinda negates the purpose.
from what i'm seeing in the reference files, the scramble bombers creates a squad that lasts 2 minutes and has a 40 second cooldown(at level 3). looks like you could maybe have up to 3 extra squads per carrier out?
siege platform gets 20->26->32 bombing damage