I choose to max E first, as it is the perfect ability to make the enemy BOT lane low in hp and your ADC push like crazy. If your adc is decent you will have won the lane. However mid to late game you cannot do much as you will probably get focused on, so that you stop annoying them, same as Teemo ;p Then, you could max Q or W second depending on your needs; for survivability go for W, for more time given to your ADC to kill the enemy ADC go for Q, although the extra time given by the upgrades of Q is 1 second form level 1 to level 5.