1. I have android kitkat installed on smartphone.

2. Every now & them junk files keeps on collecting on mobile which slow done it.

3. I have Ccleaner for it, but I don't think its that good.
Then I had tried Clean master, its looks good (but lots of ads). Does anyone have experience with this software.
Or any other better app.


4. What antivirus should I use.

 

What are these "junk files"? Kitkat is pretty strict about what it allows to write to local storage.

This - http://www.theguardian.com/technology/2014/feb/12/android-smartphone-tablet-malware-viruses - gives a good overview of the need (or not) for anti virus software.

 

Android doesn't get viruses - it's Linux! Antivirus not needed. But if you download junk - junk is what you will get!

 

Adwclenaer and malwarebytes - on demand scans - are very helpful and support any antivirus
They remove adware like http://pcspywareshield.com/guides/netmahal/ - browser hijackers and other malware