Indexing - What Is Fastest? Numeric Or Alpha Fields?

If I create an index on a field in SQL Server, what will be the most efficient (fastest) field type to index a field?  (This field will be a "Pointer" to a child table that will contain a list of codes, and their description.)

Would a Numeric field be quicker than a VarChar field?

VarChar would make it easier for a Human to decipher the raw records.  (For example, if I used a numeric the code would be 42 or 47, while the VarChar could be 'savings' or 'checking'.)

Basically I will have the following "Master" table: FieldType
---------
IDInt
NameVarChar
StatusInt -or- VarChar
Customer_TypeInt -or- VarChar

 If Customer_Type is a code that can be looked up in another table, and I index that field, would I want the "Code" to be an Int or VarChar?

SQL: Select *
From Master
Where Customer_Type = <42> or <'savings'>

 My Where clause would depend on the field type.

Thank you,
   Bryan