T-SQL Cast versus Convert

CONVERT is SQL Server specific, CAST is ANSI.

CONVERT is more flexible in that you can format dates etc. Other than that, they are pretty much the same. If you don't care about the extended features, use CAST.

EDIT:

As noted by @beruic and @C-F in the comments below, there is possible loss of precision when an implicit conversion is used (that is one where you use neither CAST nor CONVERT). For further information, see CAST and CONVERT and in particular this graphic: SQL Server Data Type Conversion Chart. With this extra information, the original advice still remains the same. Use CAST where possible.

Convert has a style parameter for date to string conversions.

http://msdn.microsoft.com/en-us/library/ms187928.aspx

To expand on the above answer_{copied by Shakti}, I have actually been able to measure a performance difference between the two functions.

I was testing performance of variations of the solution to this question and found that the standard deviation and maximum runtimes were larger when using CAST.

_{*Times in milliseconds, rounded to nearest 1/300th of a second as per the precision of the DateTime type}

You should also not use CAST for getting the text of a hash algorithm. CAST(HASHBYTES('...') AS VARCHAR(32)) is not the same as CONVERT(VARCHAR(32), HASHBYTES('...'), 2). Without the last parameter, the result would be the same, but not a readable text. As far as I know, You cannot specify that last parameter in CAST.