I'm not a huge fan of either, to be honest. I've probably heard more Lady Gaga songs than Madonna ones, but though Lady Gaga songs are pretty catchy, by no means do I think they're spectacular. In fact, I really don't like the lyrics to songs like Just Dance and Love Game. The only Lady Gaga song I've heard that I think sends a good message is Born This Way.
Kinda off-topic, but, imo too many songs these days are about sex and alcohol/drugs and partying all the time. ie Ke$ha. Tik Tok is catchy, I'll admit, but its promotion of getting drunk is horrible. No offence to Ke$ha fans.