best cleaning software

None, Mac OS X is very good at self cleaning...how much free space do you have on the hard drive? Are you running any software such as anti-virus on the machine?

Commercial cleaning software does the exact opposite - it's junkware. Go through and delete files you don't need manually. Do not delete anything from system folders, only delete media.

Go to  > About This Mac > More Info > Storage to see what is eating up your space.

Keeping your OS X up-to-date is the best tool out there, run Software Update and install all updates. Why do you think the machine needs to be cleaned, a slow running system can be caused by many things, without know even what version of OS X is installed, the amount of RAM, HD space and available HD space you are only guessing.

Please post with all of that information then we can begin troubleshooting, until then DO NOT download any "cleaning apps" you could be creating a bigger problem than you already have.

Please download, install and run Etrecheck.

Etrecheck was developed as a simple Mac diagnostic tool by a regular Apple Support forum user andtechnical support contributor named Etresoft.

Etrecheck is a small, unobstrusive app that compiles a snapshot of your entire Mac hardware system and installed software.

http://www.etresoft.com/etrecheck

Copy/paste and post its report here in another reply thread so that we have a complete profile of your Mac's hardware and installed software so we can all help with your Mac performance issues.

Please describe the problem, rather than your conclusion as to how it should be solved.

See:

Mac Maintenance Quick Assist,
Mac OS X speed FAQ,
Speeding up Macs,
How to Speed up Macs,
Macintosh OS X Routine Maintenance,
Mac troubleshooting: What to do when your computer is too slow,
Essential Mac Maintenance: Get set up,
Essential Mac Maintenance: Rev up your routines,
Maintaining OS X,
Five Mac maintenance myths and
Myths of required versus not required maintenance for Mac OS X for information.