It depends.
For torque and smoothness, mine is the Old's Rocket 350, and 455. Buick mills aren't bad either, and both smoother than the Tiac small and large journal engines, or Chevrolet, turbo fire (small), or turbojet (Mark IV) large blocks once the mileage gets high mind you.
Chevy's used to have lifter tick, and the small block 400 with it's siamesed close together bore cylinders had a sickly exhaust note. Pontiacs were known to snap timing chains.
The Chrysler original Hemi has to be on the list of course, and the old 383's and 440's also, but even a 318 used to move a mid size basic Coronet, Charger, Sattelite Sebring, Volare', or Aspen rather well, and the 360 even better.
As for Ford, the 429, and 390, the 351C (Cleveland), and 352 W (Windsor) mills. The older 390, and 429 were retired by the time pollution control standards required an EGR port, as the former blocks heads had no room to put one in. Fuel economy standards made designing new heads for smog control uneconomical. Enter the 460, which could have been a real performer, but was lower compression from the get-go. Full size Lincolns and T-Birds were very heavy, which used up all that low end torque.
Fords 400 Windsor V8 was prone to valve seal and head leaks.