I have a tiny pen from J.S. Burly's that is made of titanium, and it's been rattling around in my pocket along with steel tweezers and a steel Sebertool M4 and a P38 can opener for months. The titanium pen is scuffed beyond all belief, to the point you can't tell it was ever shiny, but there is not a single scratch deep enough to feel with my fingernail.
I also have a Raw Ti that I carry in the same pocket sometimes, and since it isn't carried all the time and has a rougher machined surface to start with, it looks brand-new -- the only places you can see any scuffing at all are on the bezel and tailcap, and again there are no significant scratches.
I would say titanium is very susceptible to scuffing, but pretty much impossible to actually damage. Stainless steel is softer, so it will self-polish in your pocket, but given the choice I'd still rather have titanium; it's lighter and it shows its "character" (i.e. age) without any risk of damage or corrosion.
All of that being said, I have a Wee NS in my watch pocket, for two reasons: one, it's sitting next to a steel pocket watch that I don't want to damage; and two, I knew I was going to get a Raw Ti but I wanted to have something made of nickel-silver because I've never seen it before. Other than the damnable tarnish that accumulates on the Wee NS, I have no complaints.