What is the best way to deal with DBNull's

DataRow row = ds.Tables[0].Rows[0];
string value = (string)row;

int? value = 5;

DataRow row = ds.Tables[0].Rows[0];
string value = row as string;

DataRow row = ds.Tables[0].Rows[0];
string value;

if (row["fooColumn"] == DBNull.Value)
{
   value = string.Empty;
}
else
{
   value = Convert.ToString(row["fooColumn"]);
}

return row["MyCol"] == DBNull.Value ? -99 : Convert.ToInt32(Row["MyCol"]);

Object.ID = DataReader["ID"] == DBNull.Value ? -99 : Convert.ToInt32(DataReader["ID"]);
Object.Name = DataReader["Name"] == DBNull.Value ? "None" : Convert.ToString(DataReader["Name"]);
Object.Price = DataReader["Price"] == DBNull.Value ? 0.0 : Convert.ToFloat(DataReader["Price"]);

string value = (
    from row in ds.Tables[0].Rows
    select row.Field<string>(0) ).FirstOrDefault();

SELECT
  ISNULL(name,'') AS name
  ,ISNULL(age, 0) AS age
FROM
  names

// Or if (row["fooColumn"] == DBNull.Value)
if (row.IsNull["fooColumn"])
{
   // use a null for strings and a Nullable for value types
   // if it is a value type and null is invalid throw a
   // InvalidOperationException here with some descriptive text.
   // or dont check for null at all and let the cast exception below bubble
   value = null;
}
else
{
   // do a direct cast here. dont use "as", "convert", "parse" or "tostring"
   // as all of these will swallow the case where is the incorect type.
   // (Unless it is a string in the DB and really do want to convert it)
   value = (string)row["fooColumn"];
}

if (row.IsNull["fooColumn"])
{
   value = string.Empty();
}
{
else
{
   value = row["fooColumn"].ToString;
}

DataRow row = ds.Tables[0].Rows[0];
string value;

if (row["fooColumn"] == DBNull.Value)
{
   value = string.Empty;
}
else
{
   value = Convert.ToString(row["fooColumn"]);
}

DataRow row = ds.Tables[0].Rows[0];
string value = row.ToString()