First and foremost Barbas CANNOT DIE! (Now maybe this is a glitch?) but I am ok with it. Barbas is the best ally in the game. Not only is he unable to die but he draws the attention of most the enemies I come across. Even Dragons focus on him and I am left to mess that dragon up with ease. His ability to draw attention in a fight is especially valuable in tight spaces like dungeons.
The only downside is the barking. Barbas barks all the %*$*^*# Time. That tends to be really annoying. If you can put up with it, fighting will be much easier with him at your side.
Last thing is to be sure not to actually finish the quest. Without giving anything away, lets just say that by finishing this quest you are forced to make some tough choices.