The Mallard sure is a beauty.
But we had some belles of the ball too:
Streamlined steamers have always been my favorite train locomotives. That Art Deco look from the 20's and 30's just seems to me to be the perfect marriage between function and form.
It looks like it's moving even when it's standing still. Modern high speed rail locos do that too, but these grand old ladies also project an image of raw power and strength that is too well hidden in the modern ones.
IMO of course.