why don't you use runehq and look up ranarrs and then it will show you what monsters.. drop them.. saves you a lot of time instead of waiting for people to answer you.
Use Zybez, RuneHq and other RuneScape help site's to tell You. And You dont need to post in a Forum to know it take's way too long.
It all depends on what one would consider to be "the best" item. If you want a dragon chain, go fight the Kalphite Queen, or Dust Devils. If you want some of that new god armour, go to that God Wars minigame.
yeah be basically said it all, like no one is gonna answer your question your question is too big, outside of the box there are hundreds of monsters!!!
I'd say the most frequant is the abbysal demons they drop whips constantly and you have more chance than getting a dchain for example.
Lol... Spiritual mages, CDD why'd you even bring up abyssal's? You may get one whip drop a day (I've had 2). I've had 27 d boot drops in a day, and a bad day is like 15 D boots.