Not intending or wanting to hijack this thread (so feel free to move if a new thread is started)

You are on the money with a goal of having the most nutritional fruit fly as something to be aspired to.

Unfortunately the scientific data comparing nutritional value of flies reared on different media are lacking, and this is a difficult subject to fully address by hobbyists as we do not generally have the availability of instrumentation and expertise to directly analyze the produced flies for various components of nutritional value.

So this leads to the information available (and that generated by frog owners) being primarily anecdotal.

Recently some commercial media is being marketed as producing "healthier" or more "nutritional" flies but again there are no analyses performed to determine values of components in the actual flies produced. Just 'cause you add it doesn't mean the flies are altered.

Additionally comparing frogs (often different species) fed on flies raised on different media (often where components / nutrients are not fully known) where the frogs are kept under different conditions / set ups is also chock full of problems in drawing firm conclusions.

There is a thread that has good / a lot of information on this exact topic started on another frog-centric forum (don't know if it's OK to mention other forums).
It should be checked out as there is some good information there.

I personally make my own media using the Frog Forum recipe on the "How To" section. I also add SuperPig to this to boost carotenoid availability.
I feel that most commercial media is probably similar in components and produce fairly equivalent flies.....but am waiting to see a real analysis of the flies prove me wrong.

Dusting and providing a varied selection of insects / larvae is probably the best way to insure good nutrition....until produced flies come with nutritional labels.