It would be nit picking because neither event was really "worse" for Bitcoin but I am going with GOX. It was the only major fiat onramp into Bitcoin so when it went offline A lot of people had no way to buy or sell anything. It disenfranchised people including myself because GOX was the entire market and it had just collapsed. All of it. FTX had no chance to collapse the entire market.

I think shortly after a random exchange called trade tree or trade hill came online. It lasted for what seemed like only a few months before fizzling out. I think Coinbase came online shortly after.