= Top
= Jungle
= mid
= Thresh
= Vayne
I'm enterpriting "top" as being "not unplayably bad early-game to make it to late". There are some harder-scaling, or at least more terrifying late-game champions, than these.
mainly comes to mind. Single scariest late-game champion in the game, provided she makes it there. But her lanning phase is among the worst in the game.
Also - not sure I'd value late-game potential much for a mid-lane pick.
Primary advantage mid-lane carries is that you'll earn more experience than bot lane, and generally more XP than all other lanes as well.
XP translates nicely into mid game power.
On average ~55 ability damage in bases per-level.
Where AA DPS only scales ~3.5 per level.
Really strong bases? Really strong mid game, really great use of the middle lane.