I would like to know that too... good question.

log cbin was the first thing that came to me

My choice would be a Basket block.

This would be my guess also. :D

My guess ... log cabin

Quiltingnonie

I love your avatar quilt. I am in Charleston, OR for the summer, where in Oregon are you?

Don't know about best selling but I'd be willing to bet SunBonnet Sue and Churn Dash are way up on the list.

Those of you that mention free patterns in newspapers and magazines are correct. I have some of the original Kansas City Star (newspaper) patterns from the 1930's. I also have patterns from Capers Weekly and the Workbasket magazine (1930-50's). In addition to these, the batting wrappers had patterns on the back. I have a few of those also. The free patterns on the internet have replaced them I guess. I know for sure our Grandmothers did not purchase patterns.

The first patterns sold were advertised and published in newspapers in the early years of the 1900s and were sold for small amounts of change - like 5 and 10 cents. The postage was a penny or two....

I rather suspect that the question has no real answer...
because the records just may not have been kept.

If the question is : "Which patterns were most made?"
Then it is probably the nine patch.

The early pioneer quilts were scrappy, and hand sewn, using one cut out square of fabric as the pattern, keeping it, and placing it on a scrap, and cutting carefully around it, and keeping the cut out pieces, perhaps sewing them together until the quilt was big enough.

There are many patterns and books that offer variations on the log cabin, if that counts as purchased patterns.