Harsh Winters bike - Steel vs aluminum frame?
I've ridden quite a few different bikes on salted roads for over three decades, and it's more a case of preferences than objective benefits.

The steel bike will get chips in the paint, then rust and look really ugly after a season or two.  It will probably take decades until it's rusted enough to make much of a structural difference, but it'll be really ugly quite fast.  Ugly bikes get stolen less, so this may be a positive if you don't care about looks.

Aluminium bikes in salt will stay rather good looking, but the steel bolts will react with the salt and aluminium and seize quite properly unless you change them all to stainless.  If you don't change them, make sure you get good at drilling out bolts and re-threading if you plan to do your own maintenance.