d20 - Rolled often, for a pass/fail result, and leading to elation or heartache on every roll. Watching them make one more tip that turns a 20 into a 2. The only die worthy of being placed in a dice jail. The only dice to have a rotation like starting pitchers, getting pulled for relief dice after failing once too often. You remember epic d20 rolls, like the time everyone was unconscious, but the monk rolled a 20 on his death save, stood up, and threw one last punch, planning to use his last ki point to disengage, and killed the boss who was about to devour everyone else. There are no epic d6 rolls.
d8 - good things are happening when you are rolling d8's. Sword and board damage, smites, superiority dice, booming blade, spirit guardians, shatter, my cheesy half-orc barbarian/rogue using strength to sneak attack with a rapier, and knowing you have more HP than wizards.