Depends very much on the specific alloy (of each) but titanium will generally get surface scratches more easily. Probably easier to polish back up, though. And "stonewashed" (tumbled) Ti looks better than scratched up steel anyway.
Neither handle heat well, but that's not too much of an issue for most "keyring" size flashlights.
Both are physically tough.
Titanium can be easily (color-)anodized, of course.
Steel will have, and maintain, better threads.