The big unit of squigs is 44 wounds and the 20 stabbas with fanatics is 25 wounds. If you compare 40 stabbas vs. 20 squigs you notice they're about the same points/wound. Beyond that the squigs are slightly faster and slightly more damage unbuffed (run & charge, better attacks, and mortal wounds) while the stabbas are more resilient (nets, better bravery, and coming back).
I spread my splattas out in a line right behind the 60 stabbas so that I could cover them but not have the splattas in combat. If my stabbas charged I lost the buff on the turn after, but the stabbas usually got charged by something.