I'm currently level 54 agility and I'm using Ape Atoll. It gives the most experience and is safer than the wilderness course. Just bring a knife and pick pineapples when you need health. Be sure to slice the pineapple instead of dicing it because it heals 6 more that way.
I just got a slayer assignment to kill 112 lesser demons and I was wondering if it would be better to use my d-long or my darklight. My levels that might relate to this are as follows: Attack: 63 Strength: 63 Defense: 62 Slayer: 48