What are the differences between the various S&P 500 ETFs? Which one is best for investing in SG?

Yes, the best & cheapest:

-in the U.S. for 0.07 to 0.08 % (tickers: VOO, IVV)

-in Europe for 0.09% (iShares Core S&P 500 UCITS ETF (Acc), tickers: CSPX, SXR8)​​​

They are managed by different companies, and they have different structures, and thus different cost structure.

The 2 best ones are ishares (IVV) and Vanguard's (VOO). Their expense ratio at extremely low at about 4basis points. Their performance difference at only about 0.01-0.02% which is fairly neligible.

Any broker that can buy shares in the US will be able to buy these ETFs. A broker that offers low commission should be your choice.