For me its Jim Steranko's S.H.I.E.L.D. and Captain America.
I also liked when Denny O'neil and Neal Adams teamed up for Green Arrow and Gren Lantern or their stint with Batman.
Their green arrow/green lantern storylines were the best. Thats what comics were all about for me. Great art and story writing. They made current events fanciful and imaginative for younger readers. Their stories tackled racism, religion, pollution, drug addiction, poverty.