what's the best program to "clean" my PC?

CCleaner Im using it for years

C:/Windows/System32/format.com

CCleaner + CCEnhancer.

After 3y a clean windows installation is not a bad idea, format :p
If you have a decent connection it isn't that painful

Backing up everything you need, formating your main hard drive (the drive where windows is installed) and reinstalling windows is the best solution because all these ''cleaners'', all they do is clean your temp folders and maybe unnecessary error logs and stuff like that, formating is the better and ''easier'' choice in my opinion.

backup - format - reinstall - best way to remove all the crap :)

You can run a program called autoruns to check what crap is starting with windows. It also shows everything it tries to start and not installed anymore (marked in red and yellow). Use some common sense disabling shit from startup though. And ccleaner works pretty nice as well in combination. That should improve boottimes at least a bit.

disable autorun programs
install os in ssd

"Clean" your PC?
Well, I recommend you to do it by yourself, watch some tutorials, use Windows tools like "cleanmgr" and "dfrgui", you will learn something about your PC...
If you don't want to do anything or you don't have time for doing it by yourself, I recommend you CCleaner.
Also, there's another program wich (i think) is better: TuneUp Utilities (AVG TuneUp or whatever...), but it's a paid program...

CCleaner, easy and efective :)

dont install CCleaner because it confclicts with VAC

From what you've said, I assume you are using Windows. The best program is your brain tbh.

Malwarebytes, do a custom scan and scan your entire PC.

Next look in task manager, startup items, research each entry and decide whether you really need them. (a lot of things look like you need them but you don't)
Next msconfig-> services (hide microsoft services)->decided if you really need all of them
In the previous 2 steps also look for any suspicious items/unneeded programs you can uninstall

Lastly, search up how to uninstall windows store apps (like microsoft money, weather blah blah) fully (one method is using powershell) if you are using W10.

have you tried /format drive c :P ?

ccleaner and glary utilities

disable unnecessary things on start up. aso check if there is something suspicious running in background. also make a full scan with malwarebytes.

ATF cleaner + CCleaner + uninstall tool(to completely remove programs)

edit and thx for the answers guys, no need more help ^^ and sry for no giveaway, just have 0.25$ xD