Try what comes with your Windows OS first
Even gamers such as myself feel compelled to try just about any type of software to improve the performance of our systems.
Truth is: "The Truth". First and foremost, protect your system for malware---whatever you use be sure it's always operating and use two or three anti-spyware programs to block and detect spyware. Use ONE anti-virus suite or stand-alone program. AVG Free 8.5 is terrific combined with a couple anti-spyware programs.
Now on to Registry cleaners, optimizers etc. None of them are necessary, period! Nothing is going to optimize your system any better than the tools that come with Windows. Why? Because people in general don't go to Programs/Accessories/System Tools and send Disk Cleaner, Disk Defragmenter and System Restore to their desktops to remember to use them! Until users become aware of what Defragging and Disk cleanup do, they run out and buy something to do all of this for them.
The nit picky stuff about leakage etc. is so infinitesimal that it is truly irrelevant. Windows Page Files? Don't mess with the settings. Since day one with Windows 98, Page Files worked just fine with Windows own system optimization capabilities, period.
Now we are up to Windows-7 and those built-in tools with again (accept for those reading this) will go unused by the average computer users in the world.
My very strong advise to all "average users". Learn the tools in Windows first-----then go spend extra money on programs that do not do a thing but register totally irrelevant minor errors (extra entries for the most part) in the Windows Registry.
Use add/remove properly. Open your Task Manager, close the relevant program that's running then remove it with Add/Remove or Programs and Features (Vista W-7).
After you install or uninstall a program, go to the directory tree, meaning all the folders under Program Files and delete the folder left behind (some are left behind) after uninstalls.
The Registry will fill-up and make your system "bog down"??? Nonsense. Again, the system can take care of itself with disk cleaner and defrag. Old entries will never grow so large as they are touted to grow to slow your system down.
Master MSCONFIG and SERVICES. Meaning, Google for the dos and don'ts of what to disable and in Services and what to uncheck in System Configuration.
If you learn the things I have just taught you above, then run your system afterwards, you'll see how much faster it performs.
All the other stuff will do some of these things for you automatically, but come-on, if you have the utilities built into System Tools, why not give them a shot first. You might surprise yourself at how well you can make your system zip along by using all the onboard tools.