Aviantese drop four noted adamant bars fairly commonly. This makes killing them fairly profitable, as each kill will on average give one adamant bar. They also drop other items worth keeping in grimy herbs and runite limbs, but the bulk of their profit comes from adamant bars, and because they are noted it means you can stay indefinitely if you aren't in need of food. Once you run out of food or you're finished, teleport out and sell your adamant bars and other items on the Grand Exchange.