To choose a registry cleaner, the most important thing is that it should be a safe and stable one. I mean it won't delete useful files from your computer and then strongly impact computer performance.
Also, you should know the importance of registry.Registry is the centre database of your computer operating system which contains information and settings for hardware, operating system software, most non-operating system software, and per-user settings. You must load the registry whenever you launch any programs on your computer. If the registry is too fat or with some errors, computer's performance will seriously be impacted.
It should has a powerful function of fixing registry errors and optimize registry. However, you just need to click simple buttons to take a full to scan your computer and find errors. Then, you still need to Click simple buttons to fix them all.
Personally, i like Wondershare Registry Optimizer which has integrated functions like clean and optimize registry, IE manager, Stat up manager, uninstall manager and back up tools.
Hope you find a proper one.