First of all...there's an awesome website about historic comic circulation numbers that is only going to become more awesome IMO.
This data in this first post comes entirely from their website.
http://www.comichron.com/Default.aspx I am going to mainly focus the numbers for the years the Legion was featured in Adventure Comics.
And awayyyy we go:
For comparison purposes, I'll start off with 1961, the year preceding the Legion moving into Adventure.
1961
Title Publisher Circulation
1) Uncle Scrooge Dell 853,928
2) Superman DC 820,000
3) Superboy DC 655,000
4) Jimmy Olsen DC 520,000
5) Lois Lane DC 515,000
6) Tarzan Dell 509,355
7) Batman DC 485,000
8) Action Comics DC 485,000
9) World's Finest Comics DC 480,000
10) Adventure Comics DC 460,000
Best selling Team Book of 1961:
12) JLA DC 335,000
Best selling Marvel Title of 1961:
39) Tales to Astonish Marvel 184,895
Best selling Marvel Team Book of 1961:
None in the top 50
1962
Title Publisher Circulation
1) Superman DC 740,000
2) Superboy DC 605,000
3) Lois Lane DC 490,000
4) Jimmy Olsen DC 470,000
5) Archie Archie 457,689
6) Casper Harvey 436,153
7) Action Comics DC 435,000
8) World's Finest Comics DC 420,000
9) Adventure Comics DC 415,000
10) Batman DC 410,000
Next best selling Team Book:
11) Justice League of America DC 340,000
Best selling Marvel Title:
44) Modeling with Millie Marvel 143,476
Best selling Marvel Team Book:
None in the top 50
The Legion/DC data for the years of 63 and 64 is unavailable due to the fact that DC didn't publish any numbers with their circulation statements in those years.
But according to at least one chart I have seen...the Legion sold well over 500k copies per month during the height of the Siegel era...the highest circulation figures ever for the Legion.
1965
Title Publisher Circulation
1) Superman DC 823,829
2) Superboy DC 672,681
3) Lois Lane DC 556,091
4) Jimmy Olsen DC 554,931
5) Action Comics DC 525,254
6) Adventure Comics DC 520,440
7) Archie Archie 467,552
8) World's Finest Comics DC 465,842
9) Batman DC 453,745
10)Disney's Comics & Stories Gold Key 410,209
Next best selling Team Book:
11) Justice League of America DC 389,285
Best selling Marvel Title:
50) Journey into Mystery Marvel 232,644
Best selling Marvel Team Book:
None in the top 50
1966
Title Publisher Circulation
1) Batman DC 898,470
2) Superman DC 719,976
3) Superboy DC 608,386
4) Lois Lane DC 530,808
5) Jimmy Olsen DC 523,455
6) World's Finest Comics DC 513,201
7) Archie Archie 491,691
8) Action Comics DC 491,135
9) Adventure Comics DC 481,234
10) Justice League of America DC 408,219
The next best selling team book(after the JLA), the best selling Marvel title, and the best selling Marvel Team Title are the all the same book for this year...
19) Fantastic Four Marvel 329,379
1967
Title Publisher Circulation
1) Batman DC 805,700
2) Superman DC 649,300
3) Superboy DC 547,100
4) World's Finest Comics DC 537,200
5) Archie Archie 484,648
6) Jimmy Olsen DC 450,700
7) Lois Lane DC 448,400
8) Detective Comics DC 425,700
9) Action Comics DC 420,900
10) Adventure Comics DC 412,800
Next best selling Team Book:
12) Justice League of America DC 385,800
Best selling Marvel Title:
14) Amazing Spider-Man Marvel 361,663
Best selling Marvel Team Book:
17) Fantastic Four Marvel 329,536
1968
Title Publisher Circulation
1) Superman DC 636,400
2) Archie Archie 566,587
3) Batman DC 533,450
4) Superboy DC 532,135
5) World's Finest Comics DC 480,115
6) Lois Lane DC 461,725
7) Jimmy Olsen DC 460,560
8) Action Comics DC 423,000
9) Betty and Veronica Archie 419,544
10) Adventure Comics DC 411,200
Next best selling Team Book:
15) Fantastic Four Marvel 344,865
Best selling Marvel Title:
12) Amazing Spider-Man Marvel 373,303
And now we get to the final year of the Adventure run, 1969 when Supergirl replaced the Legion as the lead in Adventure during the early part of the year.
1969
Title Publisher Circulation
1) Archie Archie 515,356
2) Superman DC 511,984
3) Superboy DC 465,462
4) Lois Lane DC 397,346
5) Betty and Veronica Archie 384,789
6) Action Comics DC 377,535
7) Amazing Spider-Man Marvel 372,352
8) World's Finest Comics DC 366,618
9) Batman DC 355,782
10) Adventure Comics DC 354,123
Next best selling Team Title:
12) Fantastic Four Marvel 340,363
The best selling Marvel Title was Spiderman which cracked the top 10 for the first time ever this year.