Junglers seem to have the most random impact on your games, however they are not a priority,. Best lanes to invest are top, mid and ADC just like in the real game.
Do not get sucked in to over paying for coaches or facilities, pay what you can afford and make sure you are always making more money, the predicted income / expences will not update until the game day has run so if you hire a coach or purchase a facility, remember to add their daily cost in your head to your spending ammount.