Bali is a very interesting place. That said, many areas can be very touristy. It's a big island with different types of diving that can require long van rides. Nusa Penida, in the south, is famous for pelagic fish and strong currents. It's not for the faint of heart.
Most people stay in the southern part of the island. There're several touristy areas in this area. The east coast is often overlooked as it's a fair distance from where most tourists stay. There are some good sites, including one of the best wreck dives in the world, the USS Liberty. it's a shore dive. Also look at Amed.
The north can be very laid back. Menjangan Island is the highlight. You might want to look at the large island next door, Lombok. Just past Lombok are the Gili Islands. I was in the Gili Islands years ago, so I'm sure it's much more developed now. You might also want to spend a few days in Ubud in the central part of Bali. A very interesting, cultural place. I hope this helps a little bit.