Green Dragons are a good monster to kill for their bones and hide and rune daggers, herbs, runes, level 3 clue scrolls, etc. 300xp per kill and if you get a cannon you get faster xp just wear rune crossbow and anti d shield or dragonfire shield.
Tz-Haar guards are good to kill because you can safe them and they drop obby cape, obby shield, obby mace, tokkul, etc.
Fire Giants are really good because they drop a lot of rune items such as scimitars they have very low defence so you can own them easily. Ring Of Wealth will help you have a better chance at these drops too.
you can buy knives and range yaks, those are fast xp.
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The best monster to kill in Runescape would be the King Black Dragon.
At your level, I would say killing Experiments ( Level 25 - 100Hp = 400exp per kill ) near Canfis.
There is experiments near Canfis under one of the grave stones, if you do the creature of fenkenstrain quest, it will show you how to get under it, and what gravestone your looking for, kill the level 25 ones for training they are weak, but the exp is very decent.
Corporeal Beast, Mithril Dragon, Kalphite Queen, King Black Dragon, Tormented Demons, Chaos Elemental.
Almost every Monster Drops Gold Charms but you can receive multiple charms from the level 111 Giant Rock Crab in the Chaos Tunnels.