So you want to know which deadlift muscles worked the hardest? It depends on which deadlift you were performing at the time. The different styles of deadlift can emphasize different muscle groups more than others. In the conventional deadlift the hamstring, glutes, and lower back get more work. Because of the narrow stance the quads are taken out of the movement earlier on, so the posterior chain is left to finish the movement.
On the other hand, the sumo deadlift does put slightly more emphasis on the quads. Because of the way that you set up you are able to get slightly more leg drive off the floor. However, you do not want to fall into the mindset of “squatting the bar off the floor”. You have to remember that you are deadlifting. If you try to squat the bar off the floor you will have the tendency to get too low in the set up, and that is something that you should avoid. You want ot keep your hips relatively high so that they are closer to your center of gravity. This puts you in a more mechanically advantageous position. If you squat down in sumo, as soon as you go to pull your hips will shoot up to a higher position before the bar moves, which is obviously wasted effort.
Obviously, this will vary from lifter to lifter. But the easiest way to answer the question is that conventional deadlifts use the hamstrings and lower back a bit more, and the sumo deadlift uses the quads a bit more. This really does depend on your lifting style however. Which ever movement you choose, just know that you are getting one of the best posterior chain workouts possible. There is nothing better than a good deadlift workout.