Well my roomies is a pally Tank and he off tanks for kara. Pallies can tank really well as an AOE tank. That means they can hold multiple mobs really really well. They do have a problem holding one or 2 mobs unlike the druid or the warrior. IF you want to tank as a pally you can tank all heroics if well geared but some might be a little harder the the other. For example. Shattered Halls is really easy to tank as a pally. Just get a healer and a mage and locks . You can hold multiple mobs and the lock and mage can aoe them down easily. Well Ret pallies on the other hand are good at pvp..but do not have sustained dps unlike other classes..thats why they fall behind. There is a patch coming out to upgrade pallie dps.. if you think there could be some hope.. you could go ret..but honestly.. if you go pallie... everyone will ask you to HEAL!. So do remember that.. even if you are ret you would be asked to HEAL.