at the risk of stoking the fire, i am going to defend tilapia. Tilapia is tasty, has a good texture, is nutritious, and sustainable. It often gets dumped on because it is cheap; I am sure that if retail prices reached $20/lb, it would be more en vogue. It also sees a lot of press as a substitute, and spends a lot of time as junk food like fried fish strips. Tasty, but not many people put black cod or chilean sea bass in batter and fry it for lunch. Low profile=inferior? not in this case, IMO.
Fresh tilapia is one of the only whitefish with any concentration of flavor, it is certainly more flavorful than most marine whitefish and is rivaled by only some freshwater whitefish.
Defining whether or not "more" flavor is a good thing or a bad thing is subjective, but it definately has more flavor than red snapper (lutjanus sp.) or grouper(myctoperca sp.) for example - both are so mild that they barely have any flavor, both are primarily palette texture foods. So many oceanic whitefish are the same; super mild, super tender, and almost ethereal on the palette. All of those adjectives can be read as euphemisms for "bland."
As far as freshwater fish goes, usually the selection is regional and reflects what is available to fisherman or farmers; Catfish is probably the only freshwater fish available as a fresh product nationwide, in good quality, and many people dont like catfish on principal (mostly unfounded, but this is a "don't bash tilapia" thread not a "don't bash catfish" thread). Rainbow trout is another candidate, but the biggest producer (idaho) produces crummy trout compared to the boutique producers (like rushing waters in wisconsin) so quality varies greatly.
Tilapia's texture is good, more tender like snapper than firm like grouper, it's fat content much lower than it's closest flavor rival (Catfish) and it is cheap and readily available.
Tilapia can be raised in an environmentally friendly way, which is more than i can say for the way that tiger prawns are being raised in asia.
All things considered, tilapia is indeed a good choice as a substitute for many different whitefish, but i think that we will soon see recipes written as "almond crusted tilapia, use red snapper as a substitute" because tilapia is a tasty fish.
my qualifications are: I sold fresh fish and seafood for 7 years, worked as a sushi chef for 3, and have cooked and catered at a upper-middle rung restaurant for the last two. I'm a recreational fishing enthusiast, and sit on the board of directors of a reptile and amphibian conservation/advocacy group so I am very interested in sustainability and environmental policy. I'm not saying that i've seen every fish or every dish, but i'm reasonably certain that tilapia is a more flavorful fish in the realm of whitefishes. Certainly not like sardines, anchovies, mackerals, etc, but much more flavorful than true seabass, snappers, groupers, etc.
Erik.