If you’re investing in a startup, where you are a professional investor or is it more of opportunistic angel investment, it always makes sense to buy preferred stock instead of executing a safe note. The main reason being is that you want to hold the shares as long as possible for the purposes of QSBS which if you hold shares in a C Corp for five years, you will get a significant tax exemption when you sell the stock, more than 10 million. Another reason is that you do not get standard rights like pre emptive rights, anti dilution etc. (even though YC had addressed that with a side letter.