I chose these 8 decks for my battle box because they offer a variety of strategies and play styles. After several matches though, it's clear that they aren't all on the same power level. I created a system to determine when to update decks, and eliminate them if they're non-competitive or too strong.
My selection methodology is based on a series of leagues, tournaments and matches. Each league consists of 3 tournaments. Each tournament is a double-elimination style bracket. After each tournament, sideboards are upgraded to fit the battle box meta, however I want to keep mainboards the same to avoid too much alteration. After each league, mainboards can be upgraded as long as the theme and feel of the deck doesn't change. At the end of each league, the 2 decks with the worst record will be relegated from the box and replaced by new decks. If a deck wins 2 of the 3 tournaments, it will be retired to eternal glory.