Creating Clustered Index on Integer or Varchar columns, which is better performance

Hi,

    Some one ask me the question Creating Clustered Index on Integer or Varchar columns, which is better performance?

E.g

I have a table

Employee

EmployeeID   varchar(10)

Phone    bigint

Name    varchar(50)

Deptname   varchar(50)

on which column should i create an index?

What is the difference between create clustered index on  numeric or varchar data type, why numeric is faster than varchar?