MoP by far, then WoD.
WotLK had only one good raid, Ulduar, still my personal favorite; Blackrock Foundry and Throne of Thunder are totally both on second place. Still: WotLK was beside of Ulduar horrible: ICC was a bit of MEH, it was not so bad, but also not so good. ToC was GRUESOME, Malygos was an vehicle-fight, and i knew exactly that half of my raid would die on it, always the same one, and Obsidian Sanctuary was also... it was simply a 1 boss fight: not that this is something bad, but it was to late to have any kind of impact.
WoD had Blackrock Foundry, one of the best raids ever, but also Highmaul; and this was a really bad dungeon, except the last boss, that i actually liked (even and because it also took very long).
MoP Mogushan Vault was also enjoyable; especially when you also did LFR, since lfr was not a joke-mode in MoP. In fact, there was not a single failure in raids in MoP, so i went with MoP.
Naturally MoP was also good because classes back then were enjoyable. If your class is bad, then no matter what you do, the game stays bad, no matter how good the raids are. This also made WoD loose to MoP.