“Decks to Beat” are decks that have seen prominent play in both the latest Hearthstone Tournaments and Hearthstone Ladder/Ranked play. They are extremely well refined and balanced decks.
“Decks to Watch” are decks that have a consistence presence in Tournaments and Ranked, and it’s heavily dependent on the meta. When the meta shifts, these decks can rise to become the Decks to Beat or fall out of favor.
“Others” are decks that appear sporadically, not expected by the mass and can go on to snag multiple win streaks. People may expect a Freeze Mage when they’re really facing an Echo Giants Mage (similar openers and early game), which can cause them to make costly decisions.
“Old Meta Decks” are decks that are no longer viable or seen minimal play. Either due to its core cards nerfed or simply not suitable for the current meta, no matter how much the meta shifts.