I loved doing Classic quests… once.
I hate Classic questing on alts. That’s why I get boosted on my alts.
Quest story is better in Classic than in retail. But once you do the quest once, the story is no longer exciting. The only part of the quest which remains is the chore. Go travel across the world and discover a new zone… wait, I have spent 10 hours in that zone a few months ago, there is nothing to discover. Go travel across the world and waste your time and xp/hour! Uhm, no?
Retail questing is less fun the 1st time, but it has better replayability because it is designed to be EFFICIENT. That’s one of the primary reasons you see way less boostees in retail than in Classic.