The size of the generated hash and the speed of the algorithm are not important. I’m really only interested in it being the most secure option. I don’t want to use any third party libraries either.
The version of the .NET framework I’m using if 3.5 if that makes any difference.
I would think SHA512 would be your best bet from the built-in hash algorithms. It’s the largest hash form of a very secure algorithm.
Also, don’t forget to use a salt to help protect the hash against dictionary attacks.