Well, you can look at it many different ways. One could say that herblore/prayer is the easiest because once you have supplies you can get crazy fast xp. But then again, those are probably the most expensive skills in the game. But if I had to choose the easiest skill i'd probably say cooking or fletching. Both have a relatively high xp/hr rate and are extremely quick. As for the hardest skill... I would say undoubtedly Runecrafting is. Slayer isn't too bad as its not intensive and involves combat which is enjoyable,, for most.
Although I have been noticing alot more people with the skillcape.
