It is included only in free version and you can easily disable these signatures so where is the problem ?

I would consider Avast as one of the best although some competitors such as Panda and 360 are getting better and better. But if you compare it with windows defender, anything is better. http://avastfans.com/windows-antivirus-comparison/

What you really need is good detection rates and working fileshield and webshield. You can find this in all “cheap” (free) antivirus software.

Avast popups can be easily disabled http://avastfans.com/how-to/disable-popups/

This program is free. There is nothing wrong specially if you can disable avast email signature in few easy steps.