My first thought for this scenario would be Captain America 1. Much more energetic Kirby artwork, Hitler getting seven bells knocked out of him on the cover, and a great-looking, all-time classic super-hero design.
But, having seen a high grade Marvel 1, the blue cover is very bright and attractive, and would really stand out if you saw it fresh on the newsstand.
You'd be drawn to both of them.
Overall, though, as Captain America is one of my favourite characters, easily his first appearance for me.