I think mop had the best questing, truth be told. Warlords and Legion aren't that far off, they follow kind of the same map as mop, but Warlords took it a step farther to FULLY linear (in mop you can hop to other hubs if you want, OR you can let it guide you, brilliant), and Legion goes a bit far the other way at times, as well as just not entirely having as interesting stories to me.
It's all about time and place though, the reality is you won't see the resolutions of most zones storylines (outside of vanilla/low level zones) until you do dungeons and raids and whatnot, which kind of cuts them off at the knees in some ways if the content isn't current.
For example, the whole Klaxxi storyline was fucking AWESOME, but it's got both rep gating (to awaken the paragons) AND requires you to run HoF, ToES, and SoO in order to fully appreciate what was going on with them. Killing the paragons in siege was epic and bittersweet because of all of the time you put in with them in Dread Wastes, but if you don't do any of that extra stuff your storyline basically ends at 'oh, the klaxxi seem to be in trouble and I woke like 2 dudes up.'