If by "best for my class" we mean when my favorite class was OP, then BfA hands down. The damage healers could put out was seriously overtuned. But which one was the most fun for resto shamans? I'm with @Purj on TBC, Wrath, and MoP. I'd pick Wrath out of those three. In all three, resto shamans brought great utility, but really had to leverage their kits to make a meaningful impact on the battlefield.
As a long-time rogue I basically enjoyed anything pre-BFA.
Probably had the most fun in TBC simply because I was young and green and easy to please.
But WoD has the best specific stealthy memories for me so I guess I'd have to vote for that.
i loved MoP and WoD's arms warrior. Imo every f2p xpac (cata, mop, wod, legion, vfa slands) is great for arms warrior with the slight exception of early cata where you couldnt charge in combat.