I never really came across PC guard before so cannot offer any opinion, but I do see it uses scanning engines from Kaspersky, which can only be good. As it is a full security suite it would not be advisable to run another real-time AV as well.
Don't fool yourself into thinking that if it uses the same Engine as Kaspersky that it's just as good. If the rules and defentions are not complete or up-to-date, well, the Engine wouldn't be as good,right? :-)
Honestly, I downloaded MSE (Mircosoft Security Essentials ) which seems to do the job. Here is the thing, whatever AV program you use, will pretty much be the same. Once new infection is out, in about 5 days, most of the major devlopers have a fix or/and rules to clean it out.
AVG is a pretty good AV tool but I find it has too large of a footprint, but as I never ran PC guard, I'm not sure how resorce hungry it is. I say if you already paid for PC Gaurd, Uninstal AVG and put in PC Gaurd. Once removing AVG, also remembre to use ether A)Revouninstall or B)AVG removal tool. Just to make sure nothing lingers form the pervious install
Hope this helps.