I prefer 1.
While TBC did bring some improvements to the game, it also was the beginning of many changes that seriously negatively impacted the feel of the world.
Everything relevant became condensed to a very small continent.
Crafting materials stopped feeling like you were gathering appropriate items, everything was made primarily with motes.
Flying mounts removed all danger in the world, and made PvP server combat dumb due to the lack of interaction caused by them.
Dungeons stopped feeling like real places, and instead felt like 1 hour long hallways. The “city” of tempest keep was like 4 rooms with nothing in them.
Arenas caused class balance to be focused on an individual’s ability to kill someone in 2s/3s in a small room with pillars rather then in larger objective based combat. This caused the beginning of class toolkit homogenization due to arenas being the primary gearing path in PvP.
PvP balance was incredibly bad with the new arena focus. Several classes had no functional comp to work with in 2s/3s.
The badge system was the start of the auto catch up mechanics that allowed players to jump very quickly to higher tiered content, skipping much of the game by running the intro raid (karazhan) repeatedly.
It threw out one of vanilla’s better features of having low level items retain value due to interesting/fun design on them. Any item that continued to be useful was systematically nerfed. Because of this, gearing became less interesting.
It introduced daily quests, and the rapid gold inflation caused by them (not to mention the fact that they are boring and lazy content).
Faction imbalance got worse due to blood elves being just better than draenei. (And also were better ret paladins than alliance got)
The higher level cap made TBC feel like it shrank the game rather than expanded upon it (a problem that every expansion after that repeated) by invalidating all of the previous content.
TBC legendaries were no longer a guild goal, they just dropped. (And the hunter legendary was super lazy)
TBC was where the game first felt like everything was designed from the ground up to be an efficient game mechanic rather than a living world first. Quests took you to every corner of the map. You were pointed to explore everything. Materials and dungeons were streamlined too far.
TBC did make some things better (hybrid specs gained value, guild banks were nice, the de-emphasis on consumables was appreciated), but it was the beginning of many of the things that killed WoW for me.