Ask HN: LLC or Corp for Pre-Seed, Expected Raise Startup

I'm exploring starting a company (based in California) and have fortunately gotten some strong interest from an initial funder. The company would be in a sector where securing funding is essential to even getting to a MVP, but I can do a little exploration with my own funds. Given that there's a good chance of securing funding, or at least pursuing funding in the next few months, how should I form an entity to house that exploration? LLC? C-Corp? S-Corp?

I see many posts saying that C-Corp is best for raising funding, but that LLC is easiest for an initial exploration. In this case is it best to do LLC then convert? C-Corp right now? S-Corp right now?

Any advice, including that I'm mistaken on my available option, is much appreciated!

Do you need to form an entity at all while you are exploring? I think it is best to defer C Corp formation until a 6+ figure check is on the table.