hi All, I have been using the adobe CS 5.1. What do you recommend upgrade my CS? or get the subscription on a yearly basis, thanks in advance for your input here,

The decision is ultimately yours.  You have to consider your preferences and reasons for use.

If you are using the software primarily for personal projects, then have a suite might be all you need, and the one you have now might suffice for that as well.  If you are a professional who needs to be on the cutting edge, then you probably want to have the subscription working for you.

Upgrading to a new CS means getting CS6, which is likely to be that last of the CS releases.  If you do that you pay for it one time and what you get when you pay is what you will have until it becomes obsolete somewhere off in the future, except for any corrective updates that might be provided.  It should hold up to be useful for some number of years.

If you purchase a Cloud plan, you pay for it repeatedly over time - basically a monthly fee -  but you get updates and new features as they are released.  There is always a chance that newer updates could eventually out-spec the machine you own, requiring a hardware update to continue on with new releases.