There not better, they just check for different things...The things AD-aware doesn't found , are detected by SPY-Bot and visa versa. The signature files of both include many same detections, but there are some differences. It's always better to have a layered defense anyway.
So..the best protection is offered using AD-aware and SPY-bot together. (wich I do for a long time now)
They WON'T interfier with each other. as they don't have any "residents guards" running! (in the free versions although)
And to run them on regular basis with updated sign.
Thanks for providing these links !
Waldo