The Sumo Deadlift is in no way an inferior exercise.
Both are compound exercises that load the entire posterior chain.
Which one is right for you?
This depends on your history. If you had some back soreness with one of these lifts, you may want to switch to other one. It depends on your body type: if you have relative long legs the conventional DL might be hard to perform.
Both Are Good Exercises
Do you have pain?