This thread will contain spoilers. 
I hardly ever see any discussion of which quests are worth it, which I think is a shame, since they turn up from time to time and often require a lot of effort to fulfill, but sometimes give a big reward for succeeding. A marvelous cost and benefit question -- the meat and potatoes of Civ discussion.
I don't know them all, so I will start by only discussing the ones I know.
GREED -- Take my neighbor's strategic resource? Yes, please! The only trouble is, the very lack of a resource that sparked the quest to "spawn" may be a big obstacle in the way of fulfilling the quest! But there are always longbows and cats... if you can reach them within the time limit. (150 turns on Epic, don't know if it changes with speed.) If you can't, then the question opens up of whether or not it is worth it to make a desperate attack with inferior attackers just to get the resource. And that depends on the reward, which I don't know what it is! (I will find out tonight, though.)
CRUSADE - Take a holy city? Well, it depends. The rewards are a free shrine, free "defenders" in the captured holy city (I was given macemen "defenders" when I succeeded), or 7 free religion spreads. Three macemen was pretty nice -- 315 Epic hammers, I think. Three whatever is pretty nice in general, since you're at war anyway and they're delivered right to the front. They're zero-XP, however. Seven spreads is 420 Epic hammers plus the missionary-turns and upkeep coins needed to do the spreading, but you have to have seven places to put the spreads, and due to OR, I had already diligently spread everywhere. Maybe you also get to spread to rivals, but I didn't want to risk experimenting. A shrine if it's not there yet is also good indeed. So I'd say the reward here is very flexible and quite decent, so the only question is if an attack on the holy city owner is feasible in general. (And what the dang timer is on the quest -- I forget.)
HOLY MOUNTAIN -- lolwut? No. Just no.
BUILD-A-BUNCH-OF-SWORDSMEN: Yes, I think I will. IMO This quest is ironically more valuable if you are not at war yet, since the best reward IMO is free CR1 on your swords, which is invalidated on existing swords if they are already CR1... plus, if you are at war, you want to use your swords, not stockpile them.
HORSE WHISPERING: I don't know the reward on this one, but what I do know is that I find HBR to be a sidetrack and that when I do finally pick it up, I really like having all my horsey production from just 1 or 2 specialized cities. Maybe I just need to meditate on the Way of The Me In Team more, though.
BUILD-A-BUNCH-OF-COLOSSEUMS: To my memory, I only know about this one indirectly; I've never experienced it. Apparently it's an extra happiness per colosseum if you succeed. The person who mentioned it pooh-poohed it, but since you have just put colosseums in all your major cities, you now have Notre Dame. On the downside, you just put *colloseums* in your cities (or to put it another way, you just build *Notre Dame*).
I hope this thread doesn't die on the vine like most of mine
since I'm really curious to hear people's thoughts here!

I hardly ever see any discussion of which quests are worth it, which I think is a shame, since they turn up from time to time and often require a lot of effort to fulfill, but sometimes give a big reward for succeeding. A marvelous cost and benefit question -- the meat and potatoes of Civ discussion.
I don't know them all, so I will start by only discussing the ones I know.
GREED -- Take my neighbor's strategic resource? Yes, please! The only trouble is, the very lack of a resource that sparked the quest to "spawn" may be a big obstacle in the way of fulfilling the quest! But there are always longbows and cats... if you can reach them within the time limit. (150 turns on Epic, don't know if it changes with speed.) If you can't, then the question opens up of whether or not it is worth it to make a desperate attack with inferior attackers just to get the resource. And that depends on the reward, which I don't know what it is! (I will find out tonight, though.)
CRUSADE - Take a holy city? Well, it depends. The rewards are a free shrine, free "defenders" in the captured holy city (I was given macemen "defenders" when I succeeded), or 7 free religion spreads. Three macemen was pretty nice -- 315 Epic hammers, I think. Three whatever is pretty nice in general, since you're at war anyway and they're delivered right to the front. They're zero-XP, however. Seven spreads is 420 Epic hammers plus the missionary-turns and upkeep coins needed to do the spreading, but you have to have seven places to put the spreads, and due to OR, I had already diligently spread everywhere. Maybe you also get to spread to rivals, but I didn't want to risk experimenting. A shrine if it's not there yet is also good indeed. So I'd say the reward here is very flexible and quite decent, so the only question is if an attack on the holy city owner is feasible in general. (And what the dang timer is on the quest -- I forget.)
HOLY MOUNTAIN -- lolwut? No. Just no.
BUILD-A-BUNCH-OF-SWORDSMEN: Yes, I think I will. IMO This quest is ironically more valuable if you are not at war yet, since the best reward IMO is free CR1 on your swords, which is invalidated on existing swords if they are already CR1... plus, if you are at war, you want to use your swords, not stockpile them.
HORSE WHISPERING: I don't know the reward on this one, but what I do know is that I find HBR to be a sidetrack and that when I do finally pick it up, I really like having all my horsey production from just 1 or 2 specialized cities. Maybe I just need to meditate on the Way of The Me In Team more, though.

BUILD-A-BUNCH-OF-COLOSSEUMS: To my memory, I only know about this one indirectly; I've never experienced it. Apparently it's an extra happiness per colosseum if you succeed. The person who mentioned it pooh-poohed it, but since you have just put colosseums in all your major cities, you now have Notre Dame. On the downside, you just put *colloseums* in your cities (or to put it another way, you just build *Notre Dame*).
I hope this thread doesn't die on the vine like most of mine

