I still really like Boros as a guild, and I believe Aurelia is very good, but there may not be room to play many copies due to the fierce competition
A Flash counter and or blocker, there's some very fun way to use this, especially during things where your opponent may assume they're safe to be greedy, such as on a turn-ending before untapping fully, and I agree with Loxi: players like to tap out a lot carelessly
Now you can exile that one particular artifact to your hearts content, in the exact way youd want to
Be sure to keep an eye out if you happen open Shadowborn Apostle #685, #684, or #681 as your Secret Lair bonus card because these are the most expensive variants at present
If I wanted to be scientific about it, I'd tell you to pick whichever side of the coin is facing up when you flip it