Which one is better auto Overclocking or manual Overclocking ?

Solution
auto-overclocking is a safe way to get a moderate OC on your cpu. and takes a few minutes to get it done.
manual overclocking requires a lot of testing, and you will get more out of your CPU than auto OC. but can take days to get it right.
Manual overclocking is the best, BUT, you have to educate yourself on how to do it, and I suggest you get a firm grasp on it by researching how to do it. A little information can be a dangerous thing when it comes to overclocking, I've seen many cases of Toms members frying or crippling their CPUs, so if you're not ready to invest the time into learning, stick to the Auto overclocking.