A checksum is 4 bytes, with very little chance for uniqueness, and is very easily tampered with.

Hashbytes is a 16 bytes (for MD5) or 20 bytes (for SHA1) hash value calculated over a maximum of 8000 input bytes, with a pretty good guarantee for uniqueness and in the case of SHA1 also very difficult to tamper with..

So HashBytes (SHA1) is the right choice in my opinion.