So I'm going to roll a sorc in a couple of days with a friend who is going to start playing. He's going to play a Jug tank and I was wondering which spec would be better for a duo, lightning or madness? I thought madness would be because it's instant so faster moving around (he moves around really quick, we're both mmo veterans) or lightning for the burst, just afraid by the time I get something with a cast time off it'd be overkill or dead. We've done the tank healer thing before but found me going full healing was unneccesary. Any suggestions?

You should be fine with any either choice. Sorc can heal fairly well while leveling even as a dps spec. Mind you if you plan to be offhealing your jugg tank friend alot lightning spec is probably better since it has good force management and madness does not. However madness has the instant whirlwind which is great for leveling. Personally I would go with Madness spec for leveling.