Umder the constitution, the judicial branch must try criminal cases with a ... of one's peers

The correct answer is a jury of one's peers.

This right to have criminal cases tried in front of a group of one's peers (aka other American citizens) is included in Article 3 Section 2 of the US Constitution as well as the 6th amendment. This is an important right for American citizens, as it ensures that citizens accused of a crime have the opportunity to hear their case heard in front of a group of impartial citizens.