If you spend £1,000 on a computer, why not £50 on various cleaners and janitors to keep it running smoothly? I have NetShredX and it runs fine and is comprehensive.
Internet Clean Up works well for me. It has an option to tell you every time your computer contacts someone and asks permission from you. It has the best app shredder I have used. When I use NetShredX it tells me it did a good job cleaning - so they check each others work. InterNet CleanUp also checked for spyware - but, as usual with a Mac, found nothing! Aftersurf is also good.
My trash was blocked and would not empty because of "locked" apps in it, half shredded. Tiger Cache Cleaner has a "force empty" for the trash. It was worth buying just for that. It is very simple to use. It optimizes broadband at a button touch.
CleanApp is great, but so powerful and specific you need care. It is very easy to use and shows you items by name, you thought had been shredded but were not completely. BUT it makes it look as if somethings are unused (under "cobweb" facility) so be careful, and do not erase either a file you don't know before checking, as it might underpin an application. AppZapper and AppDelete are also good, but not as comprehensive.
FontNuke claims it finds the history of several days surfing and how many MB were used, even AFTER the other apps have cleaned. It then asks if you want to delete. It closes you down and then the same history is there. Strange.
I find MacJanitor easy to use and good for other organising, but, in the end, I don't really know how good the apps work - but I do know that when testing each other out they seem to confirm the job is done. It would be ironic if the best of all was the iMac's own built in cleaners - but there are a lot of other issues, as I have mentioned. Hope this was a help.