CAST and CONVERT are similar but not the same. CAST in T-SQL offers limited (basic) data conversion functionality. I cannot see why someone would prefer one over another... It's not matter of preference, it is matter of suitability. Where CAST functionality is sufficient, you use CAST, where it's not enough (requires specific format key/switch) - use CONVERT.

For example, (especially for standards-loving J.C.) using CAST you can not explicitly convert DATETIME into string in ISO format...