Due to the new 'Guaranteed Upgrade' Mechanics of the 'Chests and Potions Update' the ideal order to buy/open chests for an Event Champion is as follows:
If you are going to buy any chests, buy at least some of them
If you are not going to buy any chests, open ONE Gold Event Chest
Open Silver Event Chests until All slots are Rare(Blue)+ OR until the Event is over and you are unable to obtain anymore Silver Event Chests
Open Gold Event Chests
The above is the ideal method for opening Event Chests, however it is extremely unlikely for anyone to obtain all Blue+ Equipment from Silver Chests alone, due to their very low drop rate. As such, realistically, there is only a very marginal detriment to opening exclusively Silver Event Chests until all the Equipment is Uncommon(Green)+, and then move onto opening Golds and Silvers once they are obtained. The following order takes this into account:
If you are going to buy any chests, buy at least some of them first
If you are not going to buy any chests, open ONE Gold Event Chest
Open Silver Event Chests until All slots are Uncommon(Green)+ OR until the Event is over and you are unable to obtain anymore Silver Event Chests
Open Gold Event Chests
Due to the new 'Guaranteed Upgrade' Mechanics of the 'Chests and Potions Update' the ideal order to buy/open chests for an Event Champion is as follows:
The above is the ideal method for opening Event Chests, however it is extremely unlikely for anyone to obtain all Blue+ Equipment from Silver Chests alone, due to their very low drop rate. As such, realistically, there is only a very marginal detriment to opening exclusively Silver Event Chests until all the Equipment is Uncommon(Green)+, and then move onto opening Golds and Silvers once they are obtained. The following order takes this into account: