My favorite is Babylon. They're amazing if you want a science victory. On my last Prince game I was at 72% literacy, and the next closest Civ was at 56%. Also, Nebby has the best leader screen and best personality. He's like an evil Bond villain. If you build a National Wonder, the right wonders and build lots of Gardens, you pop out Great Scientists like no tomorrow. That, coupled with the Enlightenment policy will easily pull you ahead of almost every Civ on the map technology wise. I had GDRs while Rome was still fighting with Musketmen. Polynesia is becoming a favorite of mine too. Most of the DLC civs are great.