I'll give it a go.
AF 15 - The Icon
FF 1 - Started what we know as the Marvel Universe
Hulk 1 - Hulk Smash
X-Men 1 - Collection of many of the most popular characters in Marveldom
ToS 39 - Tony Stark is legend
JiM 83 - Norse Gods are pretty cool
AV 1 - There is no "I" in team
FF 48 - I know it's later, but opening up the cosmos has driven many of the best storylines in Marvel, and that cover!
Daredevil 1 - Who doesn't love red Batman? This one could move up in coming years
ST 110 - I'm biased but I love Strange and bringing Magic to the Universe (plus Defenders are cool!)
Honorable Mention:
SGT Fury 1 - War title, iconic character
ASM 1 - Have to include it somewhere
AV 4 - Cap is back!
TTA 27/35 - One but not both. I FAR prefer 35 in this role but I know most tend to go with 27
FF 4 - Because yeah