Auto generated SQL Server keys - uniqueidentifier or IDENTITY

-- Start at 1 and increment by 1
CREATE TABLE IDENTITY_TEST1
(
ID INT IDENTITY(1,1) PRIMARY KEY,
TESTCOLUMN CHAR(2000) DEFAULT REPLICATE('X',2000)
)
GO

-- Start at 10 and increment by 10
CREATE TABLE IDENTITY_TEST2
(
ID INT IDENTITY(10,10) PRIMARY KEY,
TESTCOLUMN CHAR(2000) DEFAULT REPLICATE('X',2000)
)
GO

-- Start at 1000 and increment by 5
CREATE TABLE IDENTITY_TEST3
(
ID INT IDENTITY(1000,5) PRIMARY KEY,
TESTCOLUMN CHAR(2000) DEFAULT REPLICATE('X',2000)
)
GO

-- INSERT 1000 ROWS INTO EACH TEST TABLE
DECLARE @COUNTER INT
SET @COUNTER = 1

WHILE (@COUNTER <= 1000)
BEGIN
   INSERT INTO IDENTITY_TEST1 DEFAULT VALUES
   INSERT INTO IDENTITY_TEST2 DEFAULT VALUES
   INSERT INTO IDENTITY_TEST3 DEFAULT VALUES
   SET @COUNTER = @COUNTER + 1
END
GO

SELECT TOP 3 ID FROM IDENTITY_TEST1
SELECT TOP 3 ID FROM IDENTITY_TEST2
SELECT TOP 3 ID FROM IDENTITY_TEST3
GO

O/P :

1
2
3

10
20
30

1000
1005
1010

Source :http://www.mssqltips.com