Damn, please don't run 2 AV's at the same time, your probably find a drop in system efficiency
Select which on you like the best, uninstall the other
Imagine having 2 AV's battling over each other, on scanning, no wait I want to scan that, no, it's my turn, I'll scan that, no, me first
You get the idea, you don't need that frustration
Spywareblaster is totally different than an AV software, It's a passive protection, no real time protection
Again, just silently helps to protect you, please read the documenation from the link I supplied
And please only decide on one AntiVirus software, If you want a second opinion, how about once in awhile you do an Online Virus scan with something like BitDefender
P.s> I would stick with Avast, do you know how to schedule it for a weekly Virus scan?