C# WinApp ช่วยบอกข้อดีข้อเสียของการมี Interface กับไม่มี Interface หน่อยครับ

namespace TORServices.TestDatabase
{
    public class _database
    {
       public enum EnumConnectionType{ ODBC, OLEDB, SqlClient }
       public  string ConnectionString;
       public EnumConnectionType ConnectionType;
       public _database(string connStr,EnumConnectionType connType)
        {
            ConnectionString = connStr; ConnectionType = connType;
        }
        public  System.Data.DataTable Datatable(string _SQL )
        {

            System.Data.DataSet ds = new System.Data.DataSet();
            switch (ConnectionType)
            {
                case EnumConnectionType.ODBC:
                    System.Data.Odbc.OdbcConnection conn1 = new System.Data.Odbc.OdbcConnection(ConnectionString);
                    conn1.Open();
                    System.Data.Odbc.OdbcDataAdapter adapter1 = new System.Data.Odbc.OdbcDataAdapter(_SQL, conn1);
                    adapter1.Fill(ds);
                    break;
                case EnumConnectionType.OLEDB:
                    System.Data.OleDb.OleDbConnection conn2 = new System.Data.OleDb.OleDbConnection(ConnectionString);
                    conn2.Open();
                    System.Data.OleDb.OleDbDataAdapter adapter2 = new System.Data.OleDb.OleDbDataAdapter(_SQL, conn2);
                    adapter2.Fill(ds);
                    break;
                case EnumConnectionType.SqlClient:
                    System.Data.SqlClient.SqlConnection conn3 = new System.Data.SqlClient.SqlConnection(ConnectionString);
                    conn3.Open();
                    System.Data.SqlClient.SqlDataAdapter adapter3 = new System.Data.SqlClient.SqlDataAdapter(_SQL, conn3);
                    adapter3.Fill(ds);

                    break;
            }

            return ds.Tables[0];

        }
        public  System.Data.DataRow Datarow(string sql)
        {
            System.Data.DataTable dt = Datatable(sql);
            return dt.Rows[0];
        }
    }
}

namespace TORServices.TestInterface
{
    public interface iDatabase
    {
        System.Data.DataRow Datarow(string sql);
        System.Data.DataTable Datatable(string sql);
    }
    public class DataODBC : iDatabase
    {
        public string ConnectionString;
        public DataODBC(string connStr) { ConnectionString = connStr; }
        public System.Data.Odbc.OdbcConnection OdbcConnection(string connectionString = "")
        {
            System.Data.Odbc.OdbcConnection con = new System.Data.Odbc.OdbcConnection(connectionString);
            try { con.Open(); return con; }
            catch (Exception ex) { throw ex; }
        }
        public System.Data.DataRow Datarow(string sql, int rowIndax = 0)
        {
            System.Data.DataTable dt = Datatable(sql);
            return (dt != null) ? dt.Rows[0] : null;
        }
        public System.Data.DataTable Datatable(string sql)
        {
            try
            {
                System.Data.DataSet ds = new System.Data.DataSet();
                System.Data.Odbc.OdbcDataAdapter adapter1 = new System.Data.Odbc.OdbcDataAdapter(sql, OdbcConnection(ConnectionString));
                adapter1.Fill(ds);
                return ds.Tables[0];
            }
            catch { return null; }
        }
    }
    public class DataOleDb : iDatabase
    {
        public string ConnectionString;
        public DataOleDb(string connStr) { ConnectionString = connStr; }
        public System.Data.OleDb.OleDbConnection OleDbConnection(string connectionString = "")
        {
            System.Data.OleDb.OleDbConnection con = new System.Data.OleDb.OleDbConnection(connectionString);
            try { con.Open(); return con; }
            catch (Exception ex) { throw ex; }
        }
        public System.Data.DataRow Datarow(string sql, int rowIndax = 0)
        {
            System.Data.DataTable dt = Datatable(sql);
            return (dt != null) ? dt.Rows[0] : null;
        }
        public System.Data.DataTable Datatable(string sql)
        {
            try
            {
                System.Data.DataSet ds = new System.Data.DataSet();
                System.Data.OleDb.OleDbDataAdapter adapter1 = new System.Data.OleDb.OleDbDataAdapter(sql, this.OleDbConnection(ConnectionString));
                adapter1.Fill(ds);
                return ds.Tables[0];
            }
            catch { return null; }
        }
    }
    public class DataSqlClient : iDatabase
    {
        public string ConnectionString;
        public DataSqlClient(string connStr) { ConnectionString = connStr; }
        public System.Data.SqlClient.SqlConnection SqlConnection(string connectionString = "")
        {
            System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(connectionString);
            try { con.Open(); return con; }
            catch (Exception ex) { throw ex; }
        }
        System.Data.DataRow Datarow(string sql, int rowIndax = 0)
        {
            System.Data.DataTable dt = Datatable(sql);
            return (dt != null) ? dt.Rows[0] : null;
        }
        System.Data.DataTable Datatable(string sql)
        {
            try
            {
                System.Data.DataSet ds = new System.Data.DataSet();
                System.Data.SqlClient.SqlDataAdapter adapter1 = new System.Data.SqlClient.SqlDataAdapter(sql, SqlConnection(ConnectionString));
                adapter1.Fill(ds);
                return ds.Tables[0];
            }
            catch { return null; }
        }
    }


}

    public class TestDATA
    {
        public void Test()
        {
            iDatabase idata = new DataOleDb("Conn String ByToR");
            System.Data.DataTable dt1 = idata.Datatable("SQL By ToR");
            TORServices.TestDatabase._database db = new TestDatabase._database("Conn String ByToR", TestDatabase._database.EnumConnectionType.ODBC);
            System.Data.DataTable dt2 = db.Datatable("SQL By ToR");

        }
    }