What is the fish food brand that you highly recommend to others to use for their tanks?
I personally try to always recommend something that has no fillers (or the least of them) for their area. This can include foods such as Hikari, New Life Spectrum, and depending on what other brands are there sometimes even Aqueon.
I never recommend ones such as Petsmart/Petco brands, or let along Tetra. The first 3-5 items in those tend to just be fillers which is nothing valuable for your livestock and tends to just "fill them up" without letting them be vibrant, highly active, or live longer.