By default I keep the torch in the left hand in lieu of a shield, with a one handed weapon in the right hand- I find blocking is pretty reliable without a shield. If I want to use a two hander I make sure there is enough light to see by and have to know I am going to meet an enemy; as you've found Roran it is not much good trying to change weapons when they are about to hit you. If there isn't much light you can drop the torch on the floor to help illuminate a few metres around you until the enemy is dispatched, then go back to the one hander and torch combo.