Most of the novice quests will be pretty easy.
Some intermediate quests will prove to be challenging, like "My Arm's Big Adventure", but on the whole will be mildly challenging.
Some experienced-level quests could be easy for some but very difficult for others.
Master-level quests have a small chance of being easy, but if they are, their requirements will cause them to be labeled master-level. The Curse of Arrav comes to mind, but requires the completion of some rather challenging quests and some moderately high levels.
Grandmaster is rather self-explanatory. The two now are either very long with very high requirements and many puzzles (While Guthix Sleeps) or shorter with a few puzzles and a VERY hard fight (Nomad's Requiem). This level of quest should never be underestimated.
RE: If you go to your quest tab you can find options to how you want the quest list organized, if you are looking for easy quests, put it under 'difficulty'. This is to get the quest options noted above.