I spent a little time googling the subject, it seems that the Firebird was the best American sports car made. Even though the Corvette was quite popular as well it was more expensive than Trans Ams. I was very surprised to see the Corvette was neutered down a lot during that time frame (Engine wise). The Camaro was popular too, but Pontiac sold more F bodys than the Chevy counterpart. Additionally the Trans Ams had better performance than the Z28 as well (Stock). Most people don't realize that muscle cars were almost extinct after 73/74 and the F body was really the only choice. Ford vomitted out the Mustang II, and Mopar pretty much dropped out for awhile. There were some new stuff coming from the Foreign market (Datsun 240,260,280, BMW, Porshe, Mazda RX7) but none were the iconic muscle cars.
The Corvettes looked great but did not perform as they should have. The Trans Am /Firebird looked great, performed great (for the time period), they were reliable and mostly affordable (plus they had 4 seats!). When you consider how many F bodies were made 30 plus years ago, you do not see them as much unless you are drinking from a can made from recycled metal.
I t would be interesting to know how many still exist in comparison to the numbers produced. Perhaps these cars have been overlooked over the decades since, but I certainly sense a new popularity arising for them.