The difference between a physical and a synthetic ETF is the method used by the fund to replicate the performance of an index.
In a physical ETF, replication is done by investing in all the securities making up the index it replicates.
Synthetic replication ETFs invest in other assets and then exchange the performance of this basket against the index.
The replication method differs: it is direct for physical ETFs, indirect for synthetic ones.
Synthetic ETFs are sometimes considered more risky than physical ones, notably because of the counterparty risk they carry.
Physical ETFs guarantee that the investor actually holds all the underlyings that make up an index.
Physical funds are less expensive than synthetic ETFs because they invest in all the securities in the index (which is impossible as an investor).
Whatever your preference, you can benefit from the diversification and transparency of ETFs.