Miss Fortune leveling E vs Q first
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I was watching all-stars and noticed Uzi leveling E first, so I checked probuilds to see what was the most standard way to level MF. It looks like the Asians level E first while the westerners level Q. The max damage of a full channel E is about the same as the middling damage of a Q at all levels. Furthermore the CD on E is reduced from 14 seconds to 10 seconds while Q's CD is reduced from 7 to 3. So as a percentage, leveling Q first reducing the CD by a higher percent. In those ways Q is better than E. Leveling Q first allows you to bully your lane harder.
The place where E shines is in its slow. It increases from 28% to 60%. MF's slow has a 1000 cast range and 200 unit diameter. It's her best escape tool but more importantly she can throw her slow down then ult an enemy without them being able to sidestep the ult and allows a support to land some easy CC to keep them in place. Not only that, it also gives MF a waveclear ability. MF's lesser talked about weakness is poor waveclear. When E is maxed it can take a melee minion to half hp and allow MF to one shot every minion in a wave.