Serana being older is a mute factor at this point. If anything it makes her weaker due to the fact that whole time she was SLEEPING

Aela does have the side boob going but Serana has to push up bra effect going with that royal garb of hers.
But Aela doesn't complain all the time and listens to instructions/trains you and is marriable. ALL a plus since Serana snubs you and won't teach you a damn thing lol.
And the modded Aela I use does look good. even up close http://i.minus.com/i80NVorGWMiwj.jpg and http://i.minus.com/iXSc0qHis4tHe.jpg