Most engaging/exciting classic quests

[Xanthias]

Raincaller.
It started at level one and went until you raised your fletching skill enough to actually make the Trueshot longbow.
Then you had to do the parts at higher levels in order to get the Raincaller

[Haldour]

I don't know if many did the quest because the reward was absurdly bad for the efoort, but the greatest classic quest in my opinion was the holy partisan of underfoot. I remember doing this quest with my two queating pals and it took us months to finish. The tale behind it was epically ddeep. The quest took us all over norrath, keeping us on our toes the whole time. Redeeming good ol dru was probably my favorite eq memory.