I was in a similar situation, I had offers from both companies and chose the startup, but ultimately ended up at Google.
I was up with the startup for 6 months, it was not a good fit for me and I lost faith in the company quickly. A recruiter reached out to me from Google while I was there to follow up. I did not need to re-interview and they brought me in since I was still in the system as an accepted candidate (I think this stands for one year). so I got to experience the best of both worlds. I’m still at google 2 years later, I can echo the sentiments of it opening up many more doors
I was up with the startup for 6 months, it was not a good fit for me and I lost faith in the company quickly. A recruiter reached out to me from Google while I was there to follow up. I did not need to re-interview and they brought me in since I was still in the system as an accepted candidate (I think this stands for one year). so I got to experience the best of both worlds. I’m still at google 2 years later, I can echo the sentiments of it opening up many more doors