Surely it doesn't matter -the system needs both. In the Antipodean air force, the FCI (Fighter Combat Instructor = QWI) has, without doubt, greater prestige and kudos within the organisation. As an FJ trimmer myself, I acknowledge their greater tactical prestige, and their enormous value to the organisation. They will develop the tactics, and lead the first four ship into the war (if we ever have to put aside beating you lot at every sport on the planet and go to a real one!). Meanwhile, I'll still be teaching circuits. So, if you want to be known as the "sharpest knife in the drawer", put in twelve hour days and have the system burn you out by the time you are thirty, then go for QWI. If, however, you don't mind not being at the top of the tactical tree, you want a skill that opens up a much wider variety of posting and post forces jobs, and you don't want to spend six months of the year away, then being a QFI has a lot going for it.
Either way, IMHO, you can't lose. At least you have some options other than flying a desk!
Regards from down under. I'm off to watch a video of Wallabies v Lions again, before the cricket starts!
BTW It's the middle of winter here - CAVOK, 24deg C. Applications being received now from QWI's and QFI's!
SW