Gath 408 Retainer

[Morari]

So are these rewards that are supposedly better come from the quick exploration or the 18 hour one?

It's sort of both. If you have the gathering stat to do the highest 18-hour venture then
1) You have a chance at the 18-hour venture's special minion drop (and I believe there are a few other special things but the minions stand out in my memory)
2) You have a chance that you'll get a rare item from the quick venture. (I've gotten Ultima accessories, some of the rare stuff from maps among others)

When the retainer comes back from a quick venture you'll get one of three messages. You'll be told that your retainer could get rare items if it were geared better, you'll be told that your retainer has enough gear to get rare items, or finally, you'll be told that since your retainer's gear is good enough to get rare items, he found something, and then the game will give it to you.