FamilySearch has released their index of the 1940 census for NY State. An index has been available on Ancestry.com for almost 2 months for NY State. Other bloggers have been comparing indexes for other states and have found many differences. I have been following Randy Seaver on Genea-Musings and The Ancestry Insider who have really been doing great jobs at comparing the indexes. For the most part, FamilySearch has a more accurate index than Ancestry. That doesn’t mean that either one is 100% correct. That is impossible. First there could be errors by the person who gave the data to the enumerator. Those could be things as simple as giving a nickname instead of the person’s legal name. Then there are spelling errors by the original enumerator. Then we get to today and someone having to interpret the handwriting. Ancestry relied on paid indexers in India. FamilySearch used volunteers but had each record indexed twice. Then if there were any differences another person would have to decide which record was correct. The FamilySearch technique is much better and has led to a more accurate index. The FamilySearch index will remain free forever. The 1940 index on Ancestry is only guaranteed to be free until the end of 2013.
Just some short comparisons of the 2 indexes. On Ancestry my cousin Roger is spelled “Roga” and on FamilySearch he is spelled “Roger.” A further distant cousin is an Edgar D. —- and FamilySearch has it correct and Ancestry has is spelled “Edgard.” My grandfather was spelled “Archie M. Halley” on Ancestry and correctly as “Halsey” on FamilySearch. I couldn’t find my granduncle Ben Halsey on Ancestry in spite of trying various spellings. He ended up at the top of the search on FamilySearch when I searched for “Ben Halsey.” His legal name was Benjamin but he hardly ever used his full name.
My suggestion is the same as others. Use the FamilySearch index first and then if you can’t find someone try Ancestry.