Neither. There are many, many issues with these sorts of cleaning clients.
Lists of issues:
- Many of them run in the background, causing system lag and unresponsiveness, which is what these clients 'aim' to stop.
- They can have unnecessary bundled items with them, such as toolbars or adware.
- The programs themselves may be heavy on the system.
- The programs could delete vital system files by accident
Personally, I would avoid any sort of heavy system cleaning client. Some, like CCleaner are okay as they avoid the registry and delete only items are temporary (like internet files).