I'd say my favorite quests were Cleric Epic 1.0 to 2.0, Ranger Epic 1.0, and PoTime flagging and the Dragonscales Wurmslayer quest.
One quest I never forget that is non-EQ was the Hunter Epic quest in Vanilla WoW, it was long and hard and just plain epic!
It had a great story and each of the parts made you master a different part of your class or you couldn't advance, the bosses would despawn if anyone tried to help you cheese it too.
I like long quests that make you think and can take days or weeks to complete.
For me, some of the earlier quests in the starting area are the fondest. I essentially knew nothing about MMO play when I first logged into EQ for the first time. Getting that next better item was entertaining for me. I spent weeks, if not months, in Blackburrow levelling and trying to get drops i needed. I loved it. Now of course I was new and that was the excitment.
What I would like to see in the future is more questing for many different aspects of the game. I have always felt more immersed in my character when I had a quest to do, a goal to achieve. What I mean by this is not to make questing just about loot. Make also about learning your next spell or your next class skill. I feel this is the investment many look for. Yes, hitting that certain level allowing you to purchase item "x" does have a certain feel of a reward, but having a quest line or community help to obtain a goal I feel is much more fulfilling.
While I do like epic and heritage quests, I also like quests that have some humor. I remember an EQ2 quest that launched with Darklight Woods. If I wasn't such a quest hoe, I never would have found this. You had to transform into an owlbear and seduce female owlbears by dancing and grunting to lay an egg. The little owlbear companion you got at the end was delightful too.
I'm getting to old lol I remember the pally epic 1.0 made half my guild KOS in Freeport doing that one ok not half but 10 of us 4 just happened to try to help at the wrong time not knowing what we were doing heh heh killed Lady Nag, I believe was the dragon in solesk about 30 times never did get my drop either wasn't my turn or didn't drop saw my name drop t bottom of list not sure how many time because couldn't get away from work lol I actually believe I began to hate that quest so much I took a month off the get a break. I also remembe packing a ton of copper I believe helping a ranger do his quest where they kill the rabbit to find a area and my roommate doing the shawl quest for his Druid. Unfortunately it's been a long time and I've tried 10-15 other mmo's since that time and have done so many quests they all blend together for me now. All I can say was very interesting fun and agrivating at the same time. I did find a lot of EQ quests long and drawn out and the ones that were rewarding in the end were far outnumbered by those not worth doing because time/in game money/ vs reward just didn't add up. As for trade skills the racial armour was some of the best you could get prior to end game raids just very expensive to make/have made/buy. Learning a skill was also insanely expensive which was awesome because the market didn't get flooded all the time. Unless you rolled a character that had no money making skills no ports/rez/agmentation on most classes so kinda made it a class thing like enchanters were best doing jewelry above all else while classes like a paladin where you were just screwed lol tank so needed groups to kill trash no Rez worth donating for no port ot tl me echanting metals lol you killed and killed and killed then spent it all in an hour lol. My bear also really sucked at the time with work my game time was very sporadic at times. But I do miss it all and would happily do it all again. Yes very interesting times :)
I would say for me, my favorite quest in EQ was the Bard Epic 1.0. The length/difficulty of that quest really made it feel like a major accomplishment in the game for me. Also, what I really liked was that you could focus on doing some very manageable parts on your own or with a few guildies during down times. So you got a sense that you were progressing/chipping away at getting to that final goal.
The other quest I really enjoyed was the Lambent armor quests (class specific armor). What I enjoyed about this type of quest was that it required gathering multiple items to hand in to the quest giver. So again, in down times, I could focus on getting that drop to get that item. Also, being a whole armor set, once you got your one armor piece and felt that accomplishment, you had a bunch more slots to fill up.
Both quests also required you to travel all over to get the necessary items, so they sent me in areas of Norrath that I might not have explored at all.
I like the Sol Ro quest in EQ 1 and the mid-level class armor quest in Dark Age of Camelot. While easy, they gave us something that everyone could achieve.
In general, quest with specific rewards are prefered. I didn't like how Vanguard handled quest. There were way to many (like WoW) and you could choose reward. The quest just did not feel personal to the quest giver since you were just getting complete suits of armor from random people. At least the Sol Ro quest were coming from a single faction.