Pro for steel: more original
Pro for stainless: never rust
Con for steel: if you don't want it to show surface corrosion, you'll need some clear coat on it (and it might need some periodic maintenance). If you don't clear coat it, then it will look like yours did back in the late '50s
Con for stainless: if you are bending it yourself, it isn't as easy to bend as alloy steel
There is a third option: FLAPS also sell a very dark colored line, not quite black, has a tinge of green in it. I wouldn't call this "near stock" either.
I ended up buying straight steel lines, and bent them all exactly how I wanted them. I replaced my pump/carb fuel line, the vacuum line between the pump and carb base, and also the steel vacuum line mounted to the engine block on the passenger side. By bending them myself, I eliminated any question whether my fuel pump connection points are stock, as well as the fuel filter bowl location (I have a small brass fitting between the carb and the filter bowl).
My motivation to change out the old lines wasn't because of rust. It was because the lines were kinked and hand-bent. They were entirely too long. I'm happy with my new lines.
Bill
