It seems that what most people call a 'winter bike' I call a bike.
Aluminium has the advantage of not rusting, which is good when you chip the paint. Steel has the advantage of looking nicer because the tubes are thinner. Many say it is more comfortable, but to a certain extent that depends on the frame. Steel's failure mode is bending. Aluminium's failure mode is snapping.
Titanium is not as strong as steel so you need more of it, so although it's less dense than steel, a frame made of it won't be that much lighter, but infinitely more attractive to thieves.
I have a
Ribble 'Winter/Audax' frame I haven't built up yet. It will be my 'going on a ride on roads with a few sandwiches and a flask on a nice day' bike though, as it has sod all room for mudguards.
People around here commute on all sorts. I regularly see people in full overalls on fully suspended 'Argos bikes' and I also see people in full team kit on bikes that look like they cost the same as my car (they tend to ruin the just-off-to-race-look somewhat by having a rucksack though).
I've thought about swapping forks on my bike to get a front disc (most braking effort is by the front wheel, and the frame has no disc mounts) but as I can lock the wheel of my bike with the current rim brakes, I don't see the benefit - the limit to my braking appears to be the tyres, not the brakes.
If you want something reliable and robust, get something with no more gears than you need (from memory beyond eight speed cassettes, you're in to the territory of thinner chains and more problematic setup) A tourer of some sort sounds ideal.