Vanilla is always the OG, but TBC was my highlight for WoW. Wrath was fun too. I disliked some aspects in BC like Resilience and some of the gear being a little too perfect, but come on Arena, Tons of sick Raids, Heroics and tbh I thought flying was a fun feature, plus the outlands were literally designed for flight. People also point out there was too many boring daily Quests but you didnt have to do them (though I found them fairly satisfying, especially when you could unlock Netherdrakes/rays.)