| | avoid bali try lombok
Bali, at Legian and Kuta, is too crowdy and traffic jam can happen for hours. Leave that places for your comfort. Try Seminyak, Ubud, or Nusa Dua.
If Bali is not your ultimate choice, try Lombok, the eastern island of Bali. In Lombok you can go to the same name Kuta, the same place: beach. I think that Kuta, Lombok is more beautiful than Kuta, Bali. In certain side of the beach, it has white sand (actually it is brighter sand, pick a glass or bottle of the sand, take them to your hotel, and compare them to white paper. It is not white!!! LOL).
Also in Lombok, If you like an easy or just fun snorkeling and sunbathing all day long, try Gili Trawangan or other 2 Gili (I had forgotten the names). Gili means island in local, while island in Bahasa Indonesia is pulau (pull-law). Gili Trawangan is the most visited island by tourists compared to others. No car and motorbike in Gili Trawangan. It is a small island. You can bike around the island for some minutes. If you are going to Gili Trawangan from Mataram, you will pass Senggigi beach area where hotels and restaurants are available for budget. Senggigi beach is most visited by locals. About young drunk backpackers, as far as I know, the air of Lombok is "cleaner" than Bali. You may be difficult to find drugs, alcohol, or marijuana as the government restrict them hardly. Don't do drugs or smoking marijuana in Indonesia, you can be jailed as a user/consumer.
Based on your budget, if you like more cultural place, you can go to Tana Toraja (Toraja Land in South Sulawesi) where it has traditional funeral party where hundreds to thousands of people joining the party, and you can also find great Toraja traditional house: Tongkonan. Another alternative is Pulau Komodo where the Komodo dragon lives.
Hope this can help.