Which is best?

Does anyone know the best domestic (1950-1975) to drop a 350 in?

350 what? Buick, Chevy, Olds, Pontiac?

Does anyone know the best domestic (1950-1975) to drop a 350 in?

Chevy

You need as light a car as possible, to stack up against all the "big" motors. For a road car, a 2nd generation Camaro is pretty good, but a bit heavy. For a drag car, use a Vega or Monza. Early Novas (Chevy II) are popular, too. '68-'74 Novas are also popular. Whatever you decide, be sure to use a Chevy motor in a Chevy body.
Tough they're outside your target age, the '78-'87 G-bodies (Malibu, Monte Carlo) are quite good. The chassis can take a lot of power. The cars aren't too heavy. Lots of good parts available, and the cars are plentiful and cheap.

Hot Rods will put Chevy 350's in anything. Look at all those old Fords with Chevy motors. If the body was a 6 Cyl. car, you might have to do some more work than if it already had a V8. Front suspension, motor mounts, trans., driveline ect. Save your money up front so you don't get dicouragerd with the cost of a motor swap and give up on the project.