What should a Level 87 fight for exp on RuneScape

If you are a Non-member i would suggest either lesser demons since they have a low defense and drop fire runes and rune med's + loads of coins or if you want a bit of a challenge go to ice giants. Lesser Demons are in Karamja Volcano. Ice Giants are in the cave near the dwarf in the Knights Sword quest, if you have done this quest you will know where the Blurite ore is and that's where the Ice Giants are.

If you are a Member i would suggest Flesh Crawlers in The Stronghold Of Security because they drop rare herbs e.g. Grimy Ranarr, Grimy Irit and many more which will make you money a gives you quite good xp per hour, however if you have 85 Slayer go to Canif's Slayer Tower and kill the Abyssal Demons which can drop the rare Abyssal Whip which are worth about 3 - 4 mil so if you can get a full invent of Abyssal Whips that's a whopping 109200000million so there you are an instant multi-millionaire also bring lot's of food because they are a high level.