If you think Bali has heavenly waterfalls, you haven't been to Malang or Bandung.
Here's a list of my comparisons for some of my experiences Bali and Java:
1. Beaches: Beaches in Bali are spectacular, there's a good beach club on every beach and the sunsets are magical, but they are always crowded by your friendly sellers and tourists. In java most of the beaches are quiet, you can hear the sound of waves instead of the sound of sellers or some loud techno music, plus the Sunsets are a bit more magical because of the surrounding volcanoes.
2. Parties: Bali has crazy parties, anything you want is there, you want a party on the beach you can get that every night at Sandbar in Canggu, you want a party with cliff diving experience you can find it at Mrs.Sippy in Kuta, but they are always crowded and the bar is super overpriced, plus locals aren't there to teach you Bahasi curse words. In Java the clubs are usually packed with live music, cheap alcohol and friendly locals teaching you Indonesian party games. Indonesia has a lovely rock culture so don't be surprised to find crazy rock songs playing and hitting you with nostalgia and dance moves you haven't practiced in ages.
3. Cost: Yes, Bali is cheaper than most of the places you have been to, but Bali is 3 times costlier than Java.As a comparison we can compare the most common beach side snack, a coconut, costs a minimum 25,000 IDR in Bali will only cost you around 8,000 IDR in Java, friendly locals as an extra. I spent half of my trip in Java, which costed me a third of what the other half costed me in Bali.
4. Ease of travel: Bali is totally 'Touristified', so finding anything is wayy easier in Bali than in Java, but where's the thrill in that? The roads are a little more rugged, people don't speak English much, number of non-local food joints is less, but isn't travel about getting out of your comfort zone and submerging into local experiences.
5. Natural wonders: Bali and Java are both full of natural wonders, be it Active Volcanoes or Waterfalls, but Java shows a purely rugged side of wonders, less guardrails, less drone restrictions and less tourist traps.
6. Infrastructure: Bali is a small island compared to Java, Bali is only to be traveled through road, but Java has a very convenient and cheap railway system, great roads and cheap flights all around it.
7. Culture: A proper culture shock will be experienced in Java, in Bali most of the things are curated for tourists, but Java is raw, you experience weird cool things and enjoy them to the fullest.
So, overall what i would say is get out of your comfort zone and go to Java, it will give you the best BANG for your buck and push you to try different things and show you wonders not to be seen anywhere else.
Go to Bali if you're a tourist; Go to Java if you're a traveler.
I would love to upload videos of my trip, what do you guys say about that?