Bertha - not effected as much by SOA, better against attack manipulators.
+3 Fruz Bertha usually is better than Magda. It depends on the situation though. You might argue that Magda does better when facing C Beast, Pilzken Edwin etc. But such situations are very rare. Bertha is better against SOA and Attack mainpulators Bertha is even better against cards like Trish and Tula. So yeah, Normally Bertha is better than Magda.
Ya, Magda is a great card...if things like Rescue/Montana/Uppers didn't exist. She might do ok against GHEIST, as they have a lot of low power cards, but she would get eaten by Roots, who somehow convinced UR that they should have SOA, attack manip, and high power.
I would tend to say it depends on the week. If there aren't a lot of attack manip clans around one week, I would definitely go Magda. She's better than an 8 because if you consider that for an 8 power to beat a 7 power they need to do equal pills until more than 7 pills have been spent, whereas if Magda reduces a 7 to 4, then you are one entire pill ahead at only 4 pills...