What should I use to compare DBNull ? Using DBNull.Value or ToString().IsNullOrEmpty()

I can check for a DBnull on a data row using any of the methods.

Either by using

if(dr[0][0]==DBNull.Value)
//do somethin

or by doing

if(dr[0][0].ToString().IsNullOrEmpty())
//do something

In Both Cases I will be getting same result.

But Which one is conecptually right approach. Which was will use less resources