Ranged tops are high risk, high reward, usually. There are exceptions, of course, like Jayce, who has a relatively low risk laning phase, but for the most part it's true. You get to abuse melee up until they back once or twice, at which point some one like Darius is going to push for an all in as opposed to being poked out. People that can't properly get away from this are fairly screwed, which is why I'd usually only recommend going ranged top laners with an escape, like Gnar. Coming from a Darius main, Teemo is one of the easiest lanes for me, because his only saving grace is a blind and some movespeed. He can't tumble away or condemn me into a wall like Vayne, or vault off of me like Quinn, and his auto range is barely longer than my E range, meaning it's not particularly difficult to hook him, and with Darius' sticking power he isn't getting away without flash.