The quick fix at this point has too many advantageous abilities for a single weapon. Pretty much everyone believes that it needs a nerf. Which abilities should be nerfed is the question.
1. Faster uber build - Right now QF is guaranteed to get uber at the same time or quicker than any other medi gun. That makes it a boon at mid since you don't have to worry about the other team getting an uber quicker than you and pushing you with your pants down. Plus, medics don't have to manage heal orders to build quickly. The 30s uber is guaranteed. It makes windows for pushes smaller and therefore, more stalemates. I would suggest either reducing the build bonus to 12.5% or (preferably) taking it away entirely. You still get a guaranteed 40s uber. You can be beaten by kritz but kritz is supposed to hard counter qf anyway.
2. Flying medics - Problems people have outlined with this mostly involve medics being better positioned on mid now and being able to get away. I don't think this aspect should be nerfed since it adds a dynamic element to the medic class. It forces the medic to control their movement and allows for skill plays that were previously impossible.
3. Medic self heal/overbuff - One of the downsides to the qf was that the medic was not invulnerable. With the overbuff on the uber, he nearly is. I don't see a reason for keeping the overheal on the uber. Medics should avoid damage like during a kritz but with the luxury of a 300% heal rate. Focus fire kills on the med should be possible with one direct + 1 solid splash rocket.
4. Faster heal rate - This is the essence of the gun and allows teammates to get back into fights quicker. I don't really see this changing.
5. 300% heal rate while ubered - Again, the essence of the gun that should be kept, but with supporting abilities that are balanced.
6. Ability to cap while ubered - Why? Stop please.
7. No knockback while ubered - Platinum put it best. This ability takes away skilled players ability to deny the uber. Pretty much combos can walk in for free, do their damage, and get out quickly without any means of slowing them down. This ability seems like a relic of times when the quick fix was not viable all the time and needed a niche, but now that it has overheals it shouldn't need this.
8. 50% overheals - If the gun doesn't have overheals, it isn't viable. This is necessary if we want to see the quick fix in any serious capacity.