Well, gunners can use bacta's whilst running as well, no need to stop and apply the bacta canister to their wounds, so I don't see why Jedi's would have to stop to ''focus'' on their wounds to heal them.
Though in the end I don't think it matters *that* much, Passive allows the gunner to get away or try and chase the jedi.(IF you manage to prevent getting shot) Active allows the jedi to keep attacking the gunner. (Which can still get away).
I would prefer active or *fast* passive as when you need to use it it's usually too late to run away without being shot. (With visual cue of course)
(Note how I'm looking at this as pure saber vs. gunner situations, I think Jedi vs Jedi situations will require a lot less healing in comparison, or at least tend to use heals a lot less.)
As of now Jedi's use bacta's found in maps anyway, though very rarely. I've only seen (heard, rather) a few occasions where a Jedi heals mid-battle, as compared to jedi gunnar fights.
So: Active for usefulness.
Passive for.. well... balancedness?