That's a tough one. I think I would say...
1. Fantastic 3
2. Wonderworld 7
3. Hit 5
4. National 7
5. Science 2
...though the top 3 are basically interchangeable. What are your favorite Fine's?
My favorite Fine covers are Hits #1, 5, 7, 17 ...Wonderworld #7 & 8 ...and National #7 and 16. Note: I just added that National #7 to my growing list of desirable Fine books (%#$@$$&) after eye-balling your copy.
As a side note, while I revere Fine's covers I'm also impressed by Crandall's Hit covers featuring Stormy Foster (aka "re-imagining Errol Flynn as a costumed hero"), because to my artist's eye Reed Crandall had a grasp of perspective and anatomy that's second to none among comic artists of the era.
Still, what's not to love about Lou Fine's covers and interior art? The fluidity of his stylized line work is phenomenal, ...dare I say unique among GA artists.
Here is my one Lou Fine cover (hey, ya gotta start somewhere, right?)...