If two triggered abilities trigger at the same time and you control both, can you choose the order they go on the stack?

When multiple triggered abilities trigger at the same time and you control all of them, you choose the order in which they are placed on the stack. This is governed by CR 603.3b, which states that if multiple abilities trigger at the same time and are controlled by the same player, that player puts them on the stack in any order they choose.

Because the stack is last-in, first-out, the last ability you place on the stack will be the first to resolve. So if you want Ability A to resolve before Ability B, you should place Ability B on the stack first, then Ability A on top of it.

If triggered abilities are controlled by different players, the active player (the player whose turn it is) puts their triggers on the stack first, then each other player in turn order does the same (CR 603.3b). This means the non-active player's triggers end up on top and resolve first.

Concrete example: You control both Panharmonicon's doubling effect and two separate "enters the battlefield" triggers on your creatures that trigger simultaneously. You may choose to stack them so that the trigger you want to resolve first is placed on the stack last, giving you full control over resolution order.

This ordering decision is made when the triggers are placed on the stack, not when they originally trigger, so you have full information about what triggered before committing to the order (CR 603.3).