For me currently its:
The officer I find really excels in a fairly common situation where the two teams are stuck at a choke point fighting each-other through a tight corridor. It is kind of normal human reaction to play it safe, and thus what ends up happening is a lot of people kind of play the angles and pop-shot eachother, rather than re-enacting D-Day and flooding the breach with their corpses for the team.
Well the officer is uniquely equipped to fill this martyr roll. (1) You can battle command yourself plus a bunch of people at the choke-point for the health boost. (2) If you have defuser, you can activate that help prevent you from getting blown up, or if you have imp flash grenade, you toss it in the room to make it even better. Make sure to manually activate it too so it triggers faster. (3) If you can make it a little bit into the room before getting torn down you activate your distupter and it disables all the enemies weapons around you.
You will almost always die, but if your team follows your heroic example they will flood the room behind you with increased health while all the enemies weapons are disabled.
Saved a lot of caps that way.