3- ST conflicts with AVAST
No, not really.
Yes, it don't, just if you don't use AV inside.
Threatfire works OK with Avast. It's a behaviour blocker. To tell the truth, though, it seldom alerts on anything except when installing or modifying software. (Which is exactly the way it should be.)
http://www.threatfire.com/
Long time since I've used ST, and I wouldn't recommend it.
I actually replaced it with Threatfire at the suggestion of one of the more knowledgeable users at the ST forum.
Very occasionally I read about Defender actually detecting and blocking something malicious. I has its uses, I guess, but from what I've read, both SAS and MBAM are streets ahead.
It slow down the windows, working not good, it has a good idea behind, but it would slow down programs opening and closing time, also annoying some times.
If you want to pay money put it on SAS or MBAM paid versions.
2-they both are more effective than ST wich has a mediocre scanner and detection at best
4- Avast doesn't really need help but just to be sure you can help yourself downloading DR Web cureIt and be happy and safe all the time
Agreed with above things. DR.Web CureIt is great one, I love it, I use it inside IE
You can see my recommended configuration in my signature, ST is a bothering software that don't do anything more than SAS+MBAM. Keep avast for your realtime protection and just keep scanning new downloaded files with SAS and MBAM. you don't need any more realtime protection if you just browse the web and get software from trusted source, you need more protection if you download something from bad source (Keygen, Crack, download from P2P, Porn and...).
if rarely you run new risky website, you can use Sandboxie
http://www.sandboxie.com/ (it's Free).
Don't slow down your computer with so much security software, if you see I've so much security software it's because my Laptop is always at risk and I'm a tester, also I play with those programs and share resualt at other forum and my blogs and... also I've some project at my laptop that is more than $12000-$13000 and need to keep them safe.