Personally I prefer the 2nd gen due to the SD-455. Give me a 73 SD-455 and I'd be happy forever. The 73-74 SD's could easily run 13's stock. Considering what everybody else inside and outside GM produced at the time, that's pretty good. The SD's were the fastest cars from GM in 73-74.
310 hp and 390 ft-lbs make for a pretty fast car. Forged pistons, rods, and crank, with 4 bolt mains is pretty tough to beat for strength. They say that, without modification, the bottom end of the engine can handle up to 600 hp.
The heads were modified RA-IV heads.
To clairify a couple of earlier posts, no 318 ever made anything close to 310 hp and 390 ft-lbs from the factory.
Also, Firebird/Camaro and Mustang are not muscle cars. They are pony cars.
Other Firebird/TA's that I like are the 89 TTA, the 69 TA, but would also consider anything with an LS1 in it.