Bali is a lovely spot filled with culture, history, art, music and adventure surrounded by lovely nature. Another popular part of Bali is beaches and oceans. Vietnam is a lush spot filled with lot of panaromic views blended with history, adventure and tourist attraction. Travelling to Bali is an ideal spot to travel.
Both places are worth the experience, but for me, Vietnam is a safe and wonderful place. Have you ever eaten banh mi in Vietnam? I got to eat this and many other dishes while in Vietnam for a week. It's fun to sit on the back of a motorbike and enjoy street food (https://antoursvietnam.com/tours/local-night-food-tour-by-scooters-saigon/)