My current Tabletop gives us:
* The CMO
* The Navigator
* A Science Officer (not the chief, not yet)
* A Tactical/Security Officer (not the chief, but 3rd in order)
* The Engineer's Mate (next up for promotion to Chief if he ever decides to move on, or should something happen to him (insert evil laugh)).
I'd really love to have an Ops officer and an XO, but we function just fine with those as NPCs (partly because it allows GM "override" on any given away mission cuz the XO is usually there, and on any given ship mission, cuz the Captain is usually there...)
One of those always reverts to semi-PC status and whoever runs that episode keeps their character that way, and plays the Captain. Does well. The CMO is mine...
The Doc
So you think, 'Might as well,
Dance a Tango to Hell,
at least I'll have Tangoed at all.'
-- "Rent," Jonathan Larson