On my ETRADE 1099-B stock sales my grant type is indicated as "OSPS" which is not an option in "what type of investment did you sell?" What is the most accurate option?

[kelsi-cooke]

I believe that these were a combination of ESPP and RSUs that I received from a company that was purchased by the company's stock I sold.

[DavidD66]

You need to find out exactly what it was that you sold.  The tax implications of selling Employee Stock Purchase Plan (ESPP) shares and Restricted Stock Units (RSUs) are very different.  You can't just pick what you think is "the most" accurate option.   If what you sold is a combination of ESPP and RSU shares, then you will have to report them separately.