The best riding steel frame is made from titanium. And that's coming from a guy who loves his C&V steel rides.
But you will feel more difference in the geometry than you would from the frame material but it doesn't sound like you can test ride any of these so moot point there.
What do you need mounts/a rack for? You say you don't want to carry a lot of stuff so why not just do a bikepacking seat pack or something?